At this time in 1967, a congressional sub-committee headed by Senator Richard Ichord convened to investigate the AR-15/M16 and all of the issues surrounding the procurement, rights to the technical data package, chain of events to milestone decisions and malfunctioning. Colt engineers went to work making a version of their AR-15/M16 rifle that would make use of the (perceived) more reliable long stroke piston of the AK47.

The first external piston version of the M16 series rifle is the Colt Model 703. Careful examination shows that Colt engineers knew in the 1960s that to correctly make an external piston operated version of the rifle a completely new upper receiver was required and the rifle had to be designed as an external piston rifle and not converted.

The Colt Model 703 was the first external piston operated rifle of the platform. For all intents and purposes the Model 703 left the ergonomics of the AR-15 and stuck an upper on it designed around a piston operated rifle. The lower receiver remained the same as the new upper receiver could retrofit any stock lower receiver. The prototype had the Foster Sturtevant designed four-position selector offering the shooter safe, semi-auto, auto and 2 or 3 round burst.

The Colt engineers back then realized the best way to make an external piston operated rifle was to redesign the upper receiver, not to take the current one designed for direct gas impingement and turn it into a host for an operating system it was not designed for. The bolt carrier has the long stroke operating rod/piston pinned to the top of the bolt carrier. The bolt carrier has two longitude grooves on the side that fit into two slots in the upper receiver acting as guides to keep the bolt carrier group moving straight back and forth in the receiver (no carrier tilt).

The gas system utilizes a gas regulator allowing the shooter to tune the rifle for any combination of ammunition type or environmental condition. Self-regulating gas systems are more finicky due to extremes of ammunition types, propellants, as well as weather and atmospheric conditions. Allowing this all to be regulated is an excellent solution. The problem is if an untrained user messes around with the regulator not knowing how to adjust it properly, the rifle may not function, and may beat itself up from over gassing or function unreliably. It has always been a double edged sword whether to permit the soldier access to adjust gas or take a self-regulating system and try to control the ammunition that goes into it.

Then next generation Colt model LE1020 is based on the Type-C SCAR rifle but many refinements were added built on comments/criticisms of the Type C rifle. This would include making the gas system easily removed for maintenance and cleaning, elimination of the UCT finish and a simpler way to attach the carrier key to the bolt carrier, which did not require machining. Later, the steel insert would be added to the rear of the cam pin, which prevented damage to the receiver seen in all other external piston AR-series rifles.

Colt issued a report in May of 1969 titled Colt’s Automatic Rifle Model 703. The lead off into the report stated, “It is Colt’s belief that Colt’s Model 703 will demonstrate better performance and superior durability when compared to the M16/M16A1 rifle.” Nobody can be sure, all of the engineers who worked on this project are gone, but evidence points to the fact Colt was both involved in the investigation of what was in fact going wrong with the AR-15/M16 rifles in Vietnam but they also wanted to be ready with a solution if the problems pointed to the operating system of the AR-15/M16. It appears as though the Model 703 was a proactive step on Colt’s part.

According to the report, “Prototype Number 1 features a closed, adjustable gas system which is completely housed in the front sight assemble. This allows the user to optimize his weapon’s efficiency according to conditions dictated by climate or ammunition. No gas deposits are permitted to enter the breech mechanism and the result is a cleaner operating weapon. In addition, a larger extractor, a failure-free extractor spring and increased dwell time before unlocking have been incorporated.” The report also stated a list of features of the Model 703:

Better extraction through delayed unlocking and stronger extractor.
Top and side sling capability.
Adjustable gas system.
Burst control (2 or 3 rounds).
Buttstock stowage of cleaning equipment.
Simplified handguard disassembly.

Field stripped Colt Model 703. Note how the bolt carrier has rails on the side that fit in a groove inside of the upper receiver. This prevents carrier tilt. Also notice the long stroke piston operating rod connects right to the top of the bolt carrier.

Also listed were Model 703 Advantages:

Gas is exhausted behind the front sight rather than into the bolt group thereby reducing the frequency of cleaning.
Weapon can be slung over the shoulder in the assault-ready position.
Adjustable gas system compensates for ammunition and climatic conditions.
Rate of fire remains relatively constant (within ± 15 rounds/minute) at any setting.
The rifle’s upper receiver was very cumbersome when compared to that of the direct gas rifle although it weighed only 4 ounces more. All stats were comparable to the M16/M16A1. However, this rifle was never let out of the gate.

At the same time, there was another organization looking to change the direct gas operating system to a short stroke tappet system. The contract, DAAG25-68-C-0742, was awarded to Olin Mathieson Chemical Corporation’s Winchester Western Division with the mandate to create a system to retrofit existing upper receivers with “The object of this contract is to improve the combat and operating effectiveness and reliability of the existing M16A1 rifle by developing a short-stroke gas system.”

The program objectives consisted of:

Determining the functioning characteristics of 25 unmodified M16A1 rifles.
Designing a test rig to establish parameters for a short-stroke gas system.
Testing and developing two prototype short-stroke gas systems.
Conducting a 6,000 round test, with Government surveillance, on three Short-Stroke models for delivery to the Government.
Fabricating ten Short-Stroke Models for delivery to the Government.
Estimating contractor cost for retrofitting M16A1 rifles with short-stroke gas system.

The Colt Model 703 was built as a long stroke piston operation design. (Courtesy of Gary Paul Johnston)

“It is concluded from this program that the short-stroke gas system is functionally a practical system for the M16 Rifle and will significantly enhance the operating effectiveness and reliability of this rifle.”

The control rifles were 25 government furnished M16A1 rifles with the new and improved sliding weight buffers and the early non chrome lined bore/chambers. It should be noted a major issue with the reliability of the M16 in Vietnam was in fact due to the non-chroming of the chamber of the rifles. The corrosion and pitting caused a majority of the failures to extract, which were catastrophic in combat. The only way to remove the stuck cartridge case was to knock it out with a cleaning rod. Once the chamber was corroded there was not enough cleaning possible to correct the failure to extract. The barrel would have to be replaced.

The gas cylinder location was to be located 5.5 inches forward of the bolt face. The original gas port location was not used for several reasons including the need for a complete redesign and replacement of the already pinned on and costly front sight base. Additionally, a long flexible gas piston would be susceptible to damage in handling and usage, the gas piston falling outside of the handguard cap and forward portion of the handguard and probably most important was the gas to be tapped at an inconsistent low pressure portion of the pressure-time curve. The shorter gas system would permit a short and sturdy gas system and tap consistently high pressure portion of the pressure-time curve. The new gas block would be pinned to the barrel for stability and durability under the hand guard. The gas block consisted of gas cylinder housing, housing plug and utilized a plain piston. There was a new gas port drilled. The bolt carrier was modified with a solid carrier key that was reinforced by a carrier key pin that was copper brazed to the carrier key. The pin is inserted into the existing gas hole in the carrier and the carrier key screws were torqued and staked. A chamfered cam pin or a steel insert in the receiver is required to overcome peening of the receiver at the rear corner of the clearance cut for the cam pin rotation. This peening is the result of the cam pin impacting on the cam in the bolt carrier after bolt pickup and rotating into the receiver. The final design omitted the chamfer of the cam pin and opted for the steel insert, which is basically a steel screw that prevents the cam pin from damaging the aluminum receiver. There is a hole drilled in the upper receiver, on the left side where the hump is, where the cam slot is on the receiver and the screw inserted.

Shown is the way Winchester-Western dealt with the damage from the cam pin cutting into the receiver right behind the cam slot in the upper receiver by using a hardened steel screw. Colt would later adopt this concept with their steel insert they added to their receiver in late 2008 and would later be used on all of their monolithic upper receivers.

The result of the study concluded that material cost per rifle was $4.16 and labor costs (excluding burden) would be $4.13 per rifle. The value of machinery, tools and gages required (incl. benches, heat treatment and Parkerizing equipment) would be $2,064,000 and the contractor start-up costs would be $205,000. The conclusion of the contract is as follows:

The dynamic operating characteristics of the M16 rifle can be duplicated with a short-stroke gas system.
The short-stroke gas system will substantially eliminate those malfunctions associated with fouling, i.e. failure to fully open and fully close.
The M16A1 rifle with a short-stroke gas system is capable of firing a significantly larger number of rounds without cleaning and lubricating than the standard M16A1 rifle.
Information to date indicates that functionally the short-stroke gas system is a practical system for the M16A1 rifle.
Certain functional characteristics, including “fail to fire” and “fail to eject” are independent of the operating energy source (gas system), but are sensitive to other mechanical conditions.
A substantial amount of data has been generated that would be useful in further analysis of the M16A1 rifle system.

Like the results of the Colt Model 703 development, the retro fit program was quite viable. However, neither system was destined to replace that of the AR-15/M16 rifle. The findings of the numerous investigations showed what the root causes in the malfunctions were in Vietnam. In reality it was not a deficiency in the rifle system, in fact it was a good viable system destined to become one of the most prolific combat rifles of all time. It was found that the major problem, failure to extract, was caused by a combination of failing to chrome plate the chamber as well as lack of cleaning tools to maintain the rifle. Along with this there was no instruction on maintenance of the rifle. The other major issue was the untested and quantified decision to switch from IMR to Ball powder against the advice from both Gene Stoner and Colt’s. In a nutshell, the rifle could work reliably with ball propellant if it was in fact modified to do so, which is what was done: the change from a basic spring guide to a buffer that had sliding weights to prevent light strikes due to bolt carrier bounce and shot peening the bolts to increase its strength due to the higher cyclic rate that cause bolt breakage. Also, the firing pin was lightened and the disconnector strengthened. With all of these modifications there was little to no benefit in going backwards to the external pistol. The direct gas system would go on to prove itself in the late 1960s right up through the introduction of the M4. There was no further military interest in a new gas system. Although Rhino offered a retrofit kit for commercial sales in the 1980s, it never really gained momentum.

The lower handguard is removable on the LE1020 for the attachment of the M203 grenade launcher.

Right after the initial years of Gulf War 2, combat missions by Special Forces showed the newly introduced M4 carbine was about to go from a back-up rifle for those who had jobs that did not require the full length rifle but needed more than a pistol could provide, to a preferred primary combat rifle by SOCOM as well as regular Army. In the early days, SOCCOM began to experience failures of bolt breakage, and barrels rupturing, as well as failure to extract. Oddly enough, regular Army was not seeing the same issues. These reports let way into the HKM4/HK416 program that claimed to create a retrofit kit as well as a new rifle touted to “improve” combat reliability of the M4 by use of a short-stroke tappet operating mechanism. So literally the HKM4/HK416 upper receiver conversion was designed initially for SOCOM to help with their perceived problems with the M4. SOCOM had decided they needed their own rifle, not one that the Department of the Army was project manager of, which included the XM-29 program that would later be whittled down to the XM8, but one they fully controlled. SOCOM in no way wanted a weapon that was an Army weapons program – hence the commencement of the SCAR Special operations Combat Assault Rifle Program. It was also no secret that the Army did not want the SOCOM SCAR rifle; they wanted the XM8. With both rifle programs running consecutively, there was a race to get the SCAR rifle adopted before the Army could get the XM8 adopted. In the end, the XM8 program was cancelled. Any manufacturer of firearms who wanted a piece of the government sales knew the M4 was sole source from the U.S. Govt. to Colt and that the Army was happy. The only way to get into the U.S. military market was to say what they had was deficient and to open up the market to non-Colt M4 rifles.

Everybody knew that SOCOM was looking for an external piston operated rifle although it was not written that way. Colt was willing and ready to partake in the competition. They, however, would introduce and submit 3 rifles to the competition; two of which were their well proven and tested direct gas variations and the third would be Colt’s first external operated piston rifle since the Model 703 and that was in 1969. At the same time, both the government and Colt were looking into the issues with the rifle failures that SOCOM had. Was it a defect in the rifle design, quality, or was it user induced. Regardless of this outcome SOCOM wanted their own rifle.

Right side of the Colt Type-C SCAR rifle. Note the VLTOR modstock, the M1911-like ambidextrous selector lever, the Colt 1-piece upper receiver as well as the SOCOM mandated tan color. The gas system was held in place with a roll pin. One of the few criticisms SOCOM had on the rifle was the lack of ease of disassembling the operating system for maintenance and cleaning. This problem would be corrected on the next generation LE1020.

Colt submitted three rifles to the SCAR competition. Both types, A and B, were based on their combat proven direct gas system. The Type C was based on the short stroke tappet piston system. The system is simple and robust. There is an operating rod with a return spring attached, a piston and a gas cylinder sleeve. All this was held into the Type C rifle with a roll pin. Due to time constraints the roll pin was not removable for cleaning at the user level. The piston head had a tapered cone shape to it rather than the conventional flat shape. The upper receiver was the newly developed monolithic upper receiver with removable bottom rail to allow installation of the M203 grenade launcher. The carrier key was solid with no gas holes and part of the bolt carrier was machined to install the carrier key. The entire rifle was coated in UCT (Ultra Chem Tech), which is a nickel boron coating and then painted tan as per the specification. The piston operating system required an H2 buffer. The rifle used a unique and patented short throw ambidextrous selector lever and a Norgon ambidextrous magazine catch. There was an Otis Technology grip cleaning kit installed and a VLTOR modstock. The front sight base had a folding front sight that engaged and disengaged by a detent.

The Type C faired very well in the competition. Sources claim it was number two in the selection. The winner was the FN rifle. There were lessons learned by Colt from feedback on the Type C rifle that would assist them in further refinement of their piston rifle. The industry was calling upon Colt to produce an external piston operated rifle. There was growing demand in the international market for something to compete with the HK416.

The unique selector lever on the Type C SCAR as requested by SOCOM. U.S. Patent US 2005/0241470 A1 was granted on Nov. 3, 2005 to Colt’s Paul Hochstrate and the late Michael LaPlante. This was only used on the SCAR rifles.

In the secrecy that Colt is known for, they went to work on their next generation piston rifle in the 2007 time frame. This new rifle would be called the LE1020. The first major change was to have a way the operating rod and grooved piston could be removed at the user level for cleaning. On the front sight base was added a captive pin similar to that of the takedown and front pivot pin. This made it simple to remove and install. Also, to cut down on parts that could be lost, the piston was attached to the operating rod. The carrier key was simplified as well. A dowel pin was added so a standard bolt carrier could be used. The dowel pin went into a hole drilled into the gas slot in the top of the carrier and drilled into the bottom of the carrier key and the carrier key was held in place by two carrier key screws. The intent of the dowel pin was to take all of the stresses off of the carrier key screws. Barrels were offered in 10.5, 14.5 and 16.1 inches. The lower receiver went back to the standard lower receiver. The UCT finish was dropped in favor of standard Mil-Spec hard coat anodizing as well as manganese phosphate on the bolt carrier group and barrel. From 2007 to 2010, the LE1020 made its way into all the major trade shows in both the military and commercial arena. The LE1020 got a significant amount of attention from both attendees and press at SHOT Show and Colt was flooded with phone calls from customers regarding the high demand for the Colt piston rifle. At this time the controversy was in clear swing as to the question if the U.S. military is giving their warriors the best small arms available in the world. Colt’s resources were heavily involved in that fight. It is this author’s opinion that Colt higher management felt that if they introduced an external piston operated rifle, it would be an admission that their M4 was inferior. Perhaps in hindsight this author feels the better way to look at it would have been to give the customer what they asked for rather than give the business away to another company.

In 2009, Colt released for sale their first monolithic upper receiver but in the direct gas configuration called the LE6940. As expected, the rifle was an instant success. It also was the first new rifle introduced by Colt since the LE6920, which was
in the late 1990s.

In 2010, Colt introduced to the military market their refined LE1020 as the APC or Advanced Piston Carbine and for the LE market as the LE6940P. The biggest change between the LE1020 and the APC/LE6940P is the operating rod/piston. The new system was called an articulating link piston. This pivoting piston and op-rod connection compensates for deflection of the barrel during firing and due to thermal expansion. It also reduces recoil and muzzle climb during firing with the piston system closer to the bore. On the end of the piston are gas rings to seal the expansion chamber. The face of the piston is flat rather than tapered cone shaped as
was the LE1020.

The operating rod/piston, removed from the Type C SCAR upper receiver, is simple and robust. The operating rod would continue to be improved for the next two generations. The gas plug can be seen as well as the hole in the front sight base for the roll pin that held it in place. The rear sight was cut from a detachable carrying handle to make as compact and light as possible.

Added to the upper receiver is the steel insert behind the cam slot to prevent damage to the receiver. This is the same in concept to what Winchester-Western did in 1968 but Colt further refined the design to make it that much more effective
than the original.

After getting customer feedback, Colt modified the folding front sight base with a sliding lock. Customer comments came in that if they were to bump the front sight the sight would disengage causing them issues with engaging targets. Colt put a durable sliding lock that prevented this from happening.

Further testing on durability showed that the current bolt carrier design could be improved. Heavy usage showed that even with the dowel pin locating the bolt carrier key on the bolt carrier, upward recoil stresses on the carrier key screws allowed them and the dowel pin to break. Colt decided to switch to an integral bolt carrier/carrier key design with the impact area of the operating rod being on the face of the shortened integral carrier key portion of the bolt carrier. This eliminated this problem from happening.

The APC was submitted to the Individual Carbine competition. There were modifications to the lower receiver to make the rifle fully ambidextrous. The lower receiver was the new 7.62x51mm modular LE901 lower receiver with the ambidextrous bolt and magazine release. The front of the receiver was cut back to a 5.56mm configuration. The Colt entry was one of the finalists but the Individual Carbine program was cancelled due to nothing showing a significant increase in reliability over the standard M4. It is this author’s opinion that the testing in the IC program was flawed. They tested to the same 6,000 round protocol as they used for the M4. Of course they will see no major improvement. Perhaps if they pushed it out to 12,000 rounds they may have seen some significant improvements. But as the saying goes, the best is the enemy of good enough. According to the Army the M4 with its product improvement features is fully suitable for the Army. There is no requirement for anything to exceed those specifications.

The operating rod was modified to accept a larger return spring as well as the piston is now part of the operating rod. The gas cylinder is now removable by a detent pin identical to that of the takedown and pivot pins of the lower receiver.

The current APC/LE6940P rifles are what you have come to expect from Colt – durable workhorses that one can bet their life on. The APC will surely have a future in the international market and is in fact involved in testing in several countries. Unfortunately, it is the new kid on the block competing with piston operated AR rifles that have been in the field and refined for more than a decade. In time the Colt rifle will achieve a combat record and prove itself the way all of its predecessors have for the last 50 years, on the battle field.

Evolution of the piston rifle bolt carrier groups. On top is the Type C SCAR. This is UCT coated and notice the modifications required to install the carrier key. The second is also UCT coated but a simple sheer pin was added to the carrier key so any standard bolt carrier group could be used. The “skis” on the rear of the carrier were welded on the first two versions. The one shown is an early UCT coated carrier but production ones were made in standard manganese phosphate finish. The third carrier is a carrier designed specifically for the piston gun. The gas port holes removed and the “skis” machined as part of the carrier. The bottom is the final design that is a 1-piece carrier increasing the strength of the key thus extending service live dramatically.

Finalized gas system including the operating rod, the articulating link piston removed from the operating rod as well as the gas plug.

The LE1020 piston that is pyramid in shape. Bottom: The final production LE6940P uses a flat piston with the articulating link.

Current production LE6940P/APC (Advanced Piston Carbine). This refined LE1020 sports the proprietary Articulating Link Piston rod, the cam pin slot protector as well as the final production 1-piece bolt carrier. The rifle is offered in 10.5, 14.5 and 16.1 inch barrels as well as selective fire of semiautomatic only.

A historic depiction of the development of the Colt short stroke tappet system: starting on top was the original proof of concept designed by Art Daigle in a Greek hotel room. The second is the Type C SCAR system, the third is the Colt LE1020 system and on the bottom is the final LE6940P/APC system. Note the main changes had to do with the ease of disassembly and decreasing of number of components. The final two major designs was the change in the piston shape and then the implementation of the articulating link piston.

The captive pin that allows for the removal of the operating mechanism. This is probably the easiest of any of the piston operated rifles in the industry to remove/install. Start the pin inward with a cartridge or suitable tool and pull out to detent. The heavier return spring pushes the system right out of the front sight base where it is easy to grab and remove.

A number of SAAB affiliated companies were showing products at the show:

Barracuda Soft Armor

First and foremost to the community- the Barracuda Soft Armor System was showcased. This is the “Ceramic ball” system that has been growing in prominence over the last few years. For our purposes, the Soft Armor was the most interesting product, with a very informative presentation. Some attendees expressed a desire to live fire a belt fed machine gun into a Soft Armor target, however, the venue did not lend itself to firing weapons- it would have terrified both the waterfowl and the local inhabitants. This writer has extensive experience with this Soft Armor, having fired thousands of rounds of 7.62x51mm in fully automatic fire at backstops that are frighteningly thin, and not one single round ever made it even close to getting through the backstop. This is a truly
impressive product.

It’s a very simple product in many ways. Soft Armor consists of pellets of approximate 13mm diameter (1/2 inch), and they are made of aluminum dioxide and silicon dioxide. This patented mixture is mold proof, does not absorb moisture, and is static until fired upon with a projectile or fragment of a mortar round. When a projectile penetrates the outer layer, it comes into contact with the ceramic pellets, which become unsettled and fluid, tumbling around the projectile until it comes to a halt. Directly hit pellets are crushed, absorbing energy, and the remaining energy from the projectile is distributed throughout the other pellets. This is often described as similar to the effect of one ball in billiards striking many others, which absorb and distribute the divided energy. In effect, one will observe some pellets crushed to powder by the projectiles and almost instantly replaced by others around them, as the projectile is diverted off-trajectory and energy is spread throughout the assembly. A 200 round burst from a belt-fed weapon, aimed into the same area, will not penetrate!

The Barracuda Soft Armor can be put into various containers- from purpose built walls and sentry points to cloth bags for fast up-armoring ship or vehicles. “Hardening” walls becomes easier in a retrofit, by filling existing walls with the ceramics (allowing for studs and structural supports must be taken into account of course). The thickness of the ceramic pellet mass will dictate the protection level.

Barracuda- Mobile Camouflage System

The Mobile Camouflage System (MCS) can be adapted to any platform, vehicle, container or equipment that needs Stealth capabilities. The unique capability includes a possibility of lowering total fuel consumption by up to 25%. This is a multispectral, multi-layer mobile system. The MCS also can provide a cooling effect in hot climates. This flexible system is used in order to protect the vehicle while moving, and can be made of a number of different materials. It is easy to attach using systems of Velcro, straps or existing bolts on the vehicle, which Barracuda will design for. The materials are flame resistant- self-extinguishing and no bromated chemicals are used. The systems are designed for 1-2 years in service, with a shelf life of ten years in storage in controlled conditions.

Spectral Performance of the MCS:
Visual (Camouflaged)
NIR = 0.7 -2.5 µm
TIR = 3-5 µm and 8-12 µm
Radar = 1 GHz – 100 GHz

Mobile Camouflage System in green

Camouflage tents that were shown were much more than just “Camouflaged.” The observation posts/tents are an example of “Multi-Spectral Signature Management.” This simply means that the device used- in this case a tent- has properties that camouflage it from observation on a variety of levels. Visually blending into the environment, and in this case, having chemical and construction qualities that mask the tent from thermal opto-electronics. As we used to say “Camouflage is more than painting your face green, it’s appearing to be something other than what you are.” With Barracuda’s Signature Management, the tent appears to be a continuation of its surroundings- an outcropping on the ground, perhaps- with a similar thermal footprint as well as blending in visually.

Mobile Camouflage System in desert coloring

Decoy vehicles: 1192, 1208 – Barracuda was utilizing realistic, lightweight decoys of military vehicles for “Faking out” the enemy observers in their display. These were quite well done, and this writer overheard several attendees refer to the “vehicle” as if it was real, when they were at a distance and then remark and laugh about how it “Fooled them” when they got closer. The “Vehicles” serve another purpose- which Barracuda utilized here at the show- using it as an easy prop to showcase other products. Here, the team is putting the “Vehicle” into place, and then it is shown with the Mobile Camouflage System installed. It’s a lot easier to export and import these fake vehicles to trade shows and exhibitions, much like many accessory manufacturers will send AirSoft replica guns to a show.

Recent photos to emerge from Iraq show government troops with new Iranian AM50 (sometimes written as ‘AM-50′) anti-materiel rifles (AMR) and Russian ORSIS T-5000 sniper rifles. Whilst initially misidentified as the Austrian Steyr HS .50, the photos suggest that these rifles are actually an Iranian-produced copy of the HS .50, known as the AM50. In 2006-2007, Iran acquired 800 Steyr HS .50 rifles; shortly thereafter, Iranian copies of the rifle were observed.

Manufactured by the Iranian state-controlled Defence Industries Organization’s (DIO) Individual Combat Industries Group (ICIG), the AM50 is a single-shot, bolt-action anti-materiel rifle chambered for 12.7 x 99 mm (.50 BMG). The most easily distinguishable differences between the HS .50 and the AM50 are in the grip and barrel. The Iranian AM50 seems to make use of a pistol grip that ICIG produces for the S-5.56, a copy of the Chinese CQ rifle (which is itself an AR-15 clone). HS .50 rifles are derived from a Heinrich Fortmeier design developed for Steyr in 2002, now available as the Fortmeier .50 BMG. Whilst the Iranian AM50 features the modified bolt handle and muzzle brake adopted by Steyr in the production HS .50 rifles, the barrel appears to be of an evenly tapered, non-fluted design, as seen in the Fortmeier rifles, rather than the stepped, fluted design adopted by the Steyr rifles.

A soldier with the new Iranian AM50 rifle. (Yuri Lyamin)

Whilst the AM50 has been documented in use by both Iranian and Syrian government troops, and a handful have been observed in the possession of non-state armed groups in Gaza and Syria, it is only in the last few months that these pictures from Iraq have surfaced. The method by which these rifles came to be in possession of Iraqi troops is unknown, but two possibilities are more likely than others.

First, the rifles may have been captured or otherwise acquired from one of the non-state armed groups in possession of these weapons. They may have been captured from fighters from the Islamic State of Iraq and the Sham (ISIS), who are known to have captured such weapons from forces loyal to Assad, and are also operating inside Iraq. Alternatively, Iraqi troops may have acquired these rifles through the pro-government Shiite militias, who in turn may have received such rifles from Iran.

It is also possible that Iraq purchased the AM50 directly from Iran. According to a report from Reuters in February, Iraq signed a deal to buy arms and ammunition from Iran worth $195 million USD. The documents cited by Reuters included provisions for “light and medium weapons.” Whilst such a contract would violate UN sanctions against Iran, it remains a possibility that these weapons could have been delivered to Iraqi troops.

A soldier holding the new Iranian AM50 rifle. (Yuri Lyamin)

The presence of the Russian ORSIS T-5000 sniper rifles in Iraq is more readily explained, as the Iraqi government recently purchased them from Russia in a sizeable arms deal. As with the AM50, pictures of the T-5000 began to appear around March 2014.

The ORSIS T-5000 is a precision bolt-action sniper rifle fed from a detachable box magazine (either five or ten rounds). Manufactured in Moscow at Promtechnologies Group’s ORSIS1 rifle factory, the T-5000 is produced in three different calibres: 7.62 x 51 mm (.308 Winchester), .300 Winchester Magnum, and .338 Lapua Magnum. There is currently no clear indication of which calibre, or combination of calibres, Iraq has purchased.

An Iraqi soldier with a Russian ORSIS T-5000. (Yuri Lyamin)

An Iraqi soldier holding the Iranian AM50 rifle. (Yuri Lyamin)

Since 1742 an ancient device called the ballistic pendulum has been used to find the recoil level. This shoot-from type of ballistic pendulum involves free hanging the gun from wires and firing it in mid-air. The distance the gun raises is a measure of what is called free recoil energy. The shoot-at type of ballistic pendulum is used to determine the energy of a projectile. With some minor variations and the addition of modern instrumentation, we’ve been using these methods for the last three centuries.

Controllability evaluation is more challenging. In cases where everyone fires the same weapon and ammunition and tries to evaluate controllability, a great inconsistency between shooters becomes evident. Even the same shooter does not repeat the same controllability performance. Most controllability evaluations involve little more than asking shooters how quickly and accurately they felt they could get off that second or third shot. Inconsistent results are a huge frustration to the military as controllability is important to keeping a burst of full automatic fire on target.

A few years ago, the U.S. Army’s Program Manager for Small Arms saw the need for advancement in technology and awarded a study contract to Knight’s Armament Company, Titusville, Florida. Project goals included the improvement of recoil measurement techniques and a better metric for controllability.

The engineers at Knight’s began their study with a thorough review of every recoil study report available. They found that almost all the reports had the same theme. A gun follows Newton’s 3rd law of physics: “For every action, there is an equal and opposite reaction.” The force that pushes the bullet and gun gas through the barrel and out the muzzle is equal to the recoil force of the gun. The rearward velocity of the firearm and its weight are multiplied together in a formula that gives the recoil energy. It’s hard to figure out how fast the firearm is recoiling especially if there is any device on the muzzle that diverts the gun gas from going straight ahead. Muzzle brakes and even flash suppressors turn the gas to give a forward force on the weapon that slows its recoil velocity. This is why researchers generally take the easy way out and find the energy with the
ballistic pendulum.

Knight’s engineers noted that recoil studies for the military almost always focused on the shooter. Repeated input of high levels of energy into the shoulder causes bruising and very high recoil energy can cause damage to the eye. The U.S. military measures the free recoil energy of every shoulder fired weapon it fields; classifying each into categories that limit how many rounds per day can be fired. Their table shows that if a gun develops less than 15 ft-lbs, (20 Joules) of energy, unlimited firing is permitted. The M4 and M16 fit this category. The highest level on the table is 60 ft-lbs (81 Joules), above which no shoulder firing is permitted. Knight’s testing found that a typical 3½ inch 12 gauge magnum shotgun develops 59 ft-lbs of energy which is alarmingly close to the military’s maximum.

While the energy method might be useful for making decisions about how many rounds per day are appropriate, its value is limited when studying recoil. The level of free recoil energy doesn’t tell anything about how much recoil force goes slamming into the shoulder. Here’s an example with results that may surprise you. Suppose one gun has a constant 300 pound recoil force and pushes against your shoulder for 1 inch of travel. In this case, recoil energy is calculated by a simple multiplication to give 300 inch-pounds of energy. Now take a second gun that pushes with a constant load of 100 pounds over 4 inches of rearward travel. The second gun has 400 inch-pounds of energy. It’s hard to appreciate that the gun with the lower force has significantly higher free recoil energy, but it’s true. This is what is so perplexing about the study of recoil. The energy method only tells part of the recoil story and that’s why the Army supported Knight’s investigation.

At the beginning of their study, Knight’s engineers instrumented both guns and shooters with the latest accelerometers, force gages and other measurement devices. Data recovered from the tests with the new instrumentation was good and certainly usable, but not remarkably better than what had been found previously with older test equipment. Their worst surprise came when they had shooters fire at full auto and filmed the target using high speed video looking for a pattern to shot placement. They were frustrated by the inconsistencies between shooters. The project results to that point were very disappointing, showing no promise to advance the technology in recoil measurement and controllability.

One of the engineers found an old Government report that talked about replacing the human shooter with a mechanical device that mimicked the shooter’s motion during firing. The metal body parts were to be connected with springs and dampers (shock absorbers) having the same characteristics of muscle and bones. Army researchers inserted a sketch of the concept in the report, but never built it. Knight’s engineers liked the idea and took it to a higher level. They also modeled the human vibrational characteristics in order to pick the right springs and dampers and then built a mechanical device with the same characteristics. This required the use of a sophisticated analytical method called modal analysis.

To understand modal analysis, you must first accept that all bodies vibrate at their natural frequency. For example, a guitar string vibrates at a natural frequency when plucked. It is also true that most bodies – guitar strings included – have more than one natural frequency, and these can occur simultaneously. The lowest natural frequency is called the first mode of vibration, followed by the second mode, etc. Each mode is at a higher frequency than the preceding one, and each has its own shape. For all bodies, there is also a natural tendency to stop the vibration called damping. Some bodies, like the Tacoma Narrows Bridge built in 1940, didn’t have enough damping and destructed when excited at its natural frequency (YouTube shows a fascinating video of the Tacoma Narrows Bridge failure.) In contrast, there is so much damping in the human body that vibration dies out quickly. To find the natural frequencies and mode shapes, engineers input different levels of vibration into a mock up weapon being held by a shooter. Each shooter was fitted with instrumentation to study the body’s response to each level of vibration. In this way, they found the vibrational modes of what the military describes as their smallest, average, and largest size shooter. Using this information, the WRSS was built to have the same characteristics.

To be able to measure controllability, Knight’s put angular measurement devices on the WRSS in order to determine the up and down movement of the end of the barrel (pitch) as well as the side-to-side motion (yaw). The WRSS precisely tracks the point of aim during and after the firing event. For hunters this information is critical for the follow-on shot. For the military this is important for controlling bursts of automatic firing, and essential to the design of muzzle devices. A precise measurement system is invaluable in the development of devices designed to reduce muzzle motion during shooting. Why? Simply because unless there are huge performance differences in these devices, even an expert shooter can’t detect changes in performance.

Besides controllability measurements, the new shooting fixture records the force on the shooter’s shoulder, the acceleration levels (g-loads) at the buttstock and on the barrel. The new WRSS has other benefits as well. Using the acceleration data, the WRSS has already been useful in solving problems with failures in gun mounted optics and other electromechanical devices. A data plot called a Shock Response Spectrum (SRS) has been used to study how many g’s the shooter, gun, and mounted accessories must endure at various frequencies. (Remember that at 1 “g” a 10 pound body weighs 10 pounds, but when subjected to 10 g’s, that same body weighs 100 pounds.) These g-levels are important to shooter reaction and more important in the development of relatively fragile accessories like scopes, laser pointers, and night vision.

Using the WRSS fixture and SRS data plots, Knight’s engineers determined the cause of a puzzling failure of a night vision scope. The scope was tested on one gun and determined to be capable of withstanding the high shock environment, yet failed when fired from a differently designed weapon of the same caliber and weight. Why the night vision scopes failed on the second gun, but held up well on the first gun, became immediately evident on the SRS data. The SRS curve of the two guns was almost a perfect match at low frequencies, but at high frequencies where electrical equipment is susceptible to failures, the second gun showed that much higher forces were being experienced.

The US Army intends to use the WRSS in its testing laboratories, and the design has been turned over to a not-for-profit organization called the Institute of Military Technology (IMT). IMT will offer the WRSS to weapons manufacturers, government laboratories and testing facilities worldwide. Commercial firearms manufacturers may also procure the WRSS from IMT for their use.

Most readers of SAR are familiar with the current U.S. military issue M4 carbine, but some may not know why it was designated as the M4. This article is a brief history of the M4’s predecessors.

In 1938, as a result of numerous surveys of the U.S. Army Field Forces, the Chief of Infantry outlined to the Adjutant General, and the Chief of Ordnance, certain weapons requirements of the infantry. In these requirements he stated that the advisability of equipping ammunition carriers, machine gun crew members, mortar crews and administrative personnel, with a light-weight shoulder weapon. The document dated September, 1938 requested consideration by the Office of the Chief of Ordnance. An evaluation of the Chief of Infantry’s request was made in November of 1938. The use of a new light rifle was not favorably considered at that time.

With the German invasion of Poland in 1939, the Chief of Infantry resubmitted his request for the development of a light rifle. This time the suggestion was considered and by June of 1940 the War Department acted to initiate a weapon development program. By directive 00 474.5/120 from the U.S. Secretary of War, the Chief of Ordnance was ordered to undertake the development, testing, and selection of a light rifle. It was estimated that 500,000 of the new light rifles would be needed, which turned out to be a very conservative figure.

A U.S. Army armorer inspects a stack of well-used M1 carbines.

The Chief of Infantry submitted general requirements for the proposed weapon, these were:

Not less than .27 caliber.
Not more than 5-pound weight with a loaded twenty round magazine.
Effective range not less than 300 yards.
Operating system to be semiautomatic, bolt or lever action.
Five or seven round capacity, seven rounds preferred.
Fixed aperture sights, effective to 300 yards.
Ammunition to have mid-range ordinate of no more than eighteen-inches at 300 yards.
Barrel should be short.
A 1903 type sling should be used.

The Cavalry (Armored Forces) and other combat units concurred with the Infantry’s requirements. The Chief of Infantry specifically recommended that each of the following be developed for possible use:

A light semiautomatic rifle
A submachine gun type
A bolt action rifle

With the selector on an M2 carbine in the forward position (shown) the carbine fired full-automatic. The rearward position was for semiautomatic fire.

The desired characteristics for the light weight rifle were prepared by October of 1940 and were approved at an Ordnance Committee meeting. The requirements were presented to eleven manufacturers and individuals by the end of 1940 including:

The Auto-Ordnance Corporation
Colt’s Patent Fire Arms Manufacturing Company.
Hi Standard Manufacturing Company.
Johnson Automatics.
Marlin Firearms.
J.D. Peterson.
Remington Arms Company.
Savage Arms Company.
Smith & Wesson
Winchester Repeating Arms Company.

Each concern received a circular listing weapon requirements, a drawing of the new .30 carbine caliber cartridge and minimum chamber requirements. Within a few months, twenty-five corporations and individuals were invited to submit a design with testing scheduled for 8 May 1941 at Aberdeen Proving Ground. Several weapons that were submitted were immediately rejected. As a result of the preliminary testing certain changes were recommended in the original requirements. The weight was increased to 5.5 pounds and the full-automatic requirement eliminated.

The fire control components of a semiautomatic M1 (top) and the select-fire M2 carbine.

U.S. Carbine, Caliber, .30 M1

The Winchester Repeating Arms entry was the eventual winner of the light rifle trials. The Winchester carbine used a unique short-stroke tappet gas system, and was adopted as Carbine, Caliber .30, M1 in October of 1941. By the war’s end there were more carbines manufactured than any other U.S. small arm. A number of diverse companies manufactured the carbine during the war; these prime contractors were supported by hundreds of subcontractors. Many of the prime contractors involved in the carbine program had no previous gun making experience, many of them manufacturers of music boxes, automotive parts and business machinery, rallied for the war effort to manufacture 6,079,648 carbines by 1945. Although the price of the carbine varied by contractor and contract, the average cost was approximately $50 per weapon. M1 Carbine prime contractors were: Winchester, Inland (Division of General Motors), Underwood-Elliot-Fisher, National Postal Meter (A very limited number were made under the name Commercial Controls Corporation), Rock-Ola, Quality Machine and Hardware, Standard Products, Saginaw Steering Gear (Division of General Motors), International Business Machine (IBM), Irwin-Pederson Arms Company (their contract was taken over by Saginaw).

Years manufactured: M1:1941-1945 (M2: 1945 only)
Magazine capacity: fifteen and thirty round box
Caliber: .30 carbine, 110 grain round nose bullet, 1,970 fps
Cyclic rate (M2 only): 750-775 rounds per minute
Operation: gas operated, closed locked bolt, select-fire (M2)
Weight: 5.2 lbs. (M1A1 model 5.5 lbs.)
Barrel length: 18 inches
Overall length: 35.75 inches (M1A1 length, stock folded 25.75 inches; stock extended 35.75 inches)

M1 Recoil Check, designed to help control muzzle rise on the M2 in the full-automatic mode of fire. The device was secured to the barrel with a clamp.

U.S. Carbine, Caliber, .30 M1A1

To make the carbine more compact for paratrooper use, the M1 carbine was fitted with a side-folding metal buttstock and wooden pistol grip. Carbines in this configuration were designated as the M1A1. With the stock in a folded position the overall length was reduced to 25.75 inches. With the stock unfolded, the overall length of the M1A1 was the same as an M1 carbine. The M1A1 was specifically designed for airborne troops and the action was the same as an M1 carbine. The only manufacturer of the M1A1 was the Inland Division. A total of 140,591 were manufactured from 1942-45. There were no M1A1 carbines originally manufactured as select-fire M2s.

Cartridge, Carbine, Caliber .30

Winchester had also developed a new mid-range cartridge to be used in the new “light rifle.” The cartridge was designated as, Cartridge, Carbine, Caliber .30 M1 and was approved as Standard on 30 September 1941. The Ordnance Department awarded contracts to the Western Cartridge Company, Winchester Repeating Arms, Remington Arms Company, Lake City Ordnance Plant and the Kings Mills Ordnance Plant. While corrosive primers were used in World War II .30-06 and .45 ACP caliber U.S. service cartridges, the .30 caliber carbine rounds all utilized non-corrosive primers. The decision to use non-corrosive primers greatly extended the service life of the carbine’s barrel.

An early M1 and folding stock M1A1 “paratrooper” carbine.

The original configuration of the .30 caliber carbine cartridge was changed early in 1942. The original .30 caliber 110-grain projectile had a cup style base, which tests had shown was unstable during firing, and would often leave a ring of gilding metal in the forward end of the chamber. A new flat base 110-grain projectile was designed to eliminate the problem. The type of powder used in the carbine cartridge was also changed. The original DuPont powder proved to be too bulky for the small case. To achieve a higher projectile velocity a new DuPont powder was introduced. The new powder increased the carbine’s muzzle velocity to 1,970 feet per second and raised the chamber pressure to 40,000 psi.

In September of 1944, the nomenclature of the .30 carbine round was changed to Cartridge, Ball, Carbine, Caliber .30 M1. The change, adding the word “ball,” was to avoid confusion with the newly adopted tracer and grenade launching cartridges developed for the carbine.

The early characteristics of the new cartridge were:
Bullet weight: 110 grains.
Charge weight: 14.5 grains of IMR 4227
Primer: Winchester No. 116
Pressure: 31,000 psi
Muzzle velocity 1,860 feet per second.

The new specifications for the improved carbine cartridge were:
Bullet weight; 110 grains
Charge: DuPont 4809 or Hercules 3950.8B (alternate)
Primer: commercial non-corrosive
Pressure: 40,000 psi
Muzzle velocity 1,970 feet
per second

In September of 1944, the nomenclature of the .30 carbine round was changed to Cartridge, Ball, Carbine, Caliber .30 M1. The change, adding the word “ball”, was to avoid confusion with the newly adopted tracer and grenade launching cartridges developed for the carbine.

Very early box of carbine ammunition: note that the nomenclature is Caliber .30 M1 Short Rifle M-1, so that it would not be confused with M1 Garand ammo. (Courtesy of John M. Miller)

U.S. Carbine, Caliber .30, M2

The original 1940 requirements for the carbine included a select-fire feature. In order to get a new weapon developed quickly, this requirement was dropped. The select-fire M2 would not be fully developed and subsequently adopted until the fall, 1944.

Early in 1944, the Inland Division began to develop a method to convert the M1 carbine into a select-fire weapon. Two Inland engineers, Paul Hamisch and Frederick Sampson, designed a conversion that required only a few new parts along with minimum changes to the weapon’s original design. The experimental select-fire M1 carbine was designated as the T4. After extensive testing of the modified carbine, the weapon was recommended for adoption as the Carbine Caliber .30, M2 in September of 1944 and was adopted as Standard in October 1944. Subsequently, the M1 and M1A1 carbines were reclassified as Limited Standard. By the time the weapon began getting into the hands of the troops in the field the war in Europe was almost over. The M2 carbine saw little combat use in World War II.

The firepower of the M1 carbine was greatly increased with the introduction of the select-fire M2 version. Like a submachine gun, the full-automatic M2 was effective for close-in combat situations and street fighting. The M2 could also be used effectively in the semiautomatic mode at longer ranges, where a pistol caliber submachine gun could not. Original M2s were only manufactured by Inland (199,500 M2 carbines), and Winchester (17,500 M2 carbines). Early Winchester M2s were marked by over-stamping the numeral 1 on the front of the receiver with a number 2. All later manufacture M2s were factory roll-marked “M2.” Original Inland and Winchester M2s all have high serial numbers over 6,000,000. There were a few very early Inland M2s manufactured with six digit serial numbers beginning with zero. Original manufacture M2 carbines were usually factory fitted with late style features, such as the adjustable style rear sight, improved safety lever and the barrel band with the bayonet lug.

Select-fire M2 carbine with 30-round magazine and muzzle brake. The cyclic rate was approximately 750 rounds per minute. RIGHT: M3 carbine with late production M3 sniper scope. (U.S. Marine Corps National Museum)

The M2’s published cyclic rate was from 750 to 775 rounds per minute. A large capacity 30-round magazine was introduced to keep up with the M2’s high rate of fire. The carbine’s light weight together with its relatively fast cyclic rate made it somewhat difficult to control in the full-auto mode of fire. One item designed specifically for controlling muzzle rise on the M2 carbine was the M1 recoil check or muzzle brake.

Some M1 carbines were converted to the M2 configuration by using the “Kit, Conversion T17.” This kit contained all the parts needed for unit armorers to upgrade their M1 carbines to the M2 status. Many existing M1s that were converted were remarked by over-stamping the number 1 with a 2 on the receiver by hand. After World War II ended in Europe, FN Belgium was contracted to inspect and rebuild carbines, and convert some of them to the M2 configuration. The FN program was completed in 1946. Virtually all weapons returned to the U.S. were rebuilt before being placed into long term storage after the war. During the Ordnance Department rebuilding programs, a large number of M1 carbines were also rebuilt to M2 specifications. Just a few years later, the M2 carbine would see its share of combat action in the Korean Conflict.

U.S. Carbine, Caliber, .30 M3

Based on scientific experiments begun in the 1930s, the “Sniperscope, T120” was developed in late 1943. Electronic devices could distinguish objects illuminated by infrared light and make them visible in a telescope. A 6-volt light with an infrared filter mounted under the stock provided invisible light to illuminate an area up to a distance of 400 feet. This combination of a light source and telescope using infrared light became the first practical night vision sight. A handle and a switch for the light were mounted on the stock. Both the telescope and the light source got their power from a heavy, lead-acid wet cell battery carried in a canvas pack.

Before the M3 carbine and M1 sniperscope were type-classified, they were known as the T3 and T120, respectively. The M3 was a carbine fitted with a mount designed to accept an infrared sight for use at night. It was initially used with the M1 sniperscope, an active infrared sight, and saw action in 1945 with the Army during the invasion of Okinawa. An improved M2 sniperscope extended the effective nighttime range of the M3 carbine out to 100 yards. Both the M1 and M2 sniperscopes had the light source located below the stock.

Select-fire M2 carbine with 30-round magazine and muzzle brake. The cyclic rate was approximately 750 rounds per minute. RIGHT: M3 carbine with late production M3 sniper scope. (U.S. Marine Corps National Museum)

The original T-3 version of the carbine was complicated, requiring a number of unique parts to mount the sniperscope. Eventually it was decided to design a simple kit that would enable a standard M1 or M2 carbine to be easily converted to use night vision sights in the field. The special mounting parts would be included with the sight sets. A new flash hider was added to conceal the user’s position. Mass production of the improved infrared night vision system began in 1950 with the “20,000 volt Set No. 1.” This could be mounted on any M1 or M2 carbine, making it an “M3” Carbine. The M3 sniperscope had a large active infrared spotlight mounted on top of the scope body itself, allowing its use with the operator in a prone position. The revised M3 had an effective range of around 125 yards. The improvements in this system included better electronics, resulting in better vision, but were still limited. Fog and rain further reduced the weapon’s effective range. Heavy weight and short battery life remained major shortcomings.

The U.S. M1 and M2 carbines remained in U.S. Army service until the M14 was accepted as their standard weapon in 1957. However, the service life of the carbine had not ended. The U.S. Air Force and Navy still issued them, and the carbine would see more action in the Vietnam War. Large numbers of carbines were provided to many allies and some former enemies as military aid.

The Syrian conflict continues to yield interesting expedient small-arm designs. ARES has received YouTube video links that document Syrian rebel forces manufacturing anti-materiel rifles (AMRs), of which there appear to be two variants. They are both home-made bolt-action anti-materiel rifles similar to, and possibly inspired by, home-made and custom hobbyist-type rifles found in other parts of the world, most notably the U.S. The examples shown are chambered for the Russian 12.7 x 108 mm machine gun round, and are referred to in the videos as the Nimr 2. They were manufactured in the workshops of Katibat Abu Asad al-Nimr, a group associated with the Hazzm Movement.

The tubular receiver is constructed out of steel, and is shown being machined in a mill or drill machine, with extensive hand-finishing whilst held in a bench vice. A length of M1913 rail is attached to its upper surface. A simple rectangular trigger-mechanism housing (with rotating trigger-bar safety) and magazine well appears to be welded onto the underside of the receiver. The magazine is also fabricated from sheet steel, and is seen in one of the videos being matched up to the magazine well to establish the proper seating depth and angle of presentation of the round. The bolt (whose locking arrangement is unclear) and long, tubular firing pin are also milled components, finished using an angle-grinder, and even the single chambered muzzle-brake is built from scratch using welded sheet steel. One variant features a custom wrap-around wooden stock and a fixed tubular bipod, whilst the other has an off-the-shelf plastic AK-type pistol grip and home-made skeletal buttstock and folding bipod.

An unusual feature on the pistol-gripped example is the camouflage sleeve cover shown being slipped over the barrel and receiver. This cover incorporates a flap dust-cover for the bolt handle slot to protect the otherwise-open action. The barrel used on both variants is the only significant factory-produced component, and was originally made for the Chinese W-85 heavy machine gun, available commercially from Norinco and previously documented in Syria. The lack of a factory-produced muzzle-brake may imply that these barrels were not cannibalised from complete weapons, but rather sourced as spare parts. The telescopic sight is also likely to be Chinese, resembling some cheaply-made models in the 20x magnification range available online. The test fire of the barrelled action in the first video shows a large muzzle-flash, but nothing from the unused machine gun gas port, which suggests that it has been sealed off. The complete weapon is later test-fired several times with apparent success, although its accuracy cannot be assessed.

An anti-materiel rifle (AMR) being worked in a bench vise. (YouTube video)

Machining the receiver of a home-made anti-materiel rifle (AMR). (YouTube video)

Scribing markings onto a home-made anti-materiel rifle (AMR). (YouTube video)

The completed anti-materiel rifle (AMR) with a camouflage sleeve. (YouTube video)

The completed anti-materiel rifle (AMR) with a camouflage sleeve. (YouTube video)

The accuracy of the AR-15/M16 has always been top rate. For the longest time, when one would think of a long range designated marksman rifle (DMR) you would think of something in 7.62x51mm NATO and more than likely bolt action. During the Vietnam War, it was seen that there is a benefit to having a semiautomatic DMR-type rifle so the accurized M14 appeared. In the calm of the Cold War, little attention was paid to small arms; money was going into nuclear weapons and advanced aircraft. Since the Vietnam War, U.S. troops encountered little combat and small arms would remain virtually unchanged. After 9/11 all that would change. Now with the Global War On Terrorism, infantry battles would be back rather than the high tech air war, which really was the First Gulf War. Prior to that, former Army Colonel Mark Westrom, former President of ArmaLite, Inc. conceived a 5.56x45mm SPR (Special Purpose Rifle); originally envisioned by Westrom to be in 18 inch, 20 inch and 22 inch barrels. The SPR as initially designed was to be an upper receiver that would be adaptable to current M4/M4A1 carbines that would fill two roles. First as a light sniper rifle and then, if need be, it could be used as a light machine gun. There was again no one rifle or carbine available that would fit this particular role so SOCOM would build it. Unfortunately it stopped, at least for a short period of time.

The concept sat dormant for years until SOCOM revived the concept in the 1990s as an initiative by the 5th Special Forces Group. They envisioned the SPR as a Special Purpose Receiver that drops on a standard M16/M4-type lower receiver. This receiver was to be highly accurized and would shoot a new type of 5.56x45mm round – one that would go on to be the most accurate 5.56mm cartridge in the world. The SPR upper receiver would provide a lightweight, compact, long-range precision fire and light support capability to the small Special Operation Forces groups that were not in a position to receive support from aircraft or artillery.

Modified M12 Mod 1. It has the fixed A1 stock replaced with an LMT SOPMOD stock with a six position receiver extension. Although the MK12-series SPRs all came with fixed stocks from Crane, Indiana, once the rifles went to their assigned units modifications were made by the users. Also the Ops, Inc. sounds suppressor is attached. Note the Harris bipod.

SOPMOD Programs Office at the Naval Surface Warfare Center, Crane, Indiana, drafted the requirements desired and went to work soliciting and testing the concept at hand. In late 1998 and throughout 1999, the 5th Special Forces Group collaborated with the U.S. Army Marksmanship Unit (USAMU) at Fort Benning, Georgia, to develop initial prototypes of this new requirement. During the program, SOPMOD funded several prototypes that were made and tested by the USAMU working closely with the 5th Special Forces.

The first SPR prototypes were tested with handloaded ammunition and the concept was solidified with the requirements being realistic and achievable. Several match grade projectiles were tested with weights as high as 88 grains. After rigorous accuracy testing, the 73-grain boat tail match open tip bullet manufactured by Berger was chosen for the SPR program. However, due to the immediate requirement for ammunition to go along with the SPR upper receiver, the Berger factory was in the process of moving and could not deliver the bullets in the needed quantities. With this kink in the chain, a new bullet was needed to fit the requirement. The new bullet would be the Sierra 77-grain Boat Tail Match King. Jeff Hoffman, president of Black Hills Ammunition was charged with designing and producing the ammunition that would both maintain match accuracy and combat reliability of theM16A2 rifle. Based on these findings, in October of 1999, the SPR was validated as part of the SOPMOD requirement. First requirements called for the drop-in SPR for the M4A1 carbine along with the match grade ammunition. Conceptually, there would be a modified M4A1 carbine that would have precision match grade accuracy in a lightweight rifle that could provide semi- or automatic firepower on demand. The rifle is designed as a match grade rifle but if the need would arise the heavy barrel would provide fully automatic suppressive fire.

Finalized MK12 Mod 1 rifle. Note the M16A1 lower receiver that would be equipped with a Knight’s Armament two stage selective fire trigger group. This rifle differs from the Mod 0 with the handguard and backup sights. The handguard used is the Knight’s Armament M4 Match Free-Floating Rail Adapter System (KAC part number 99167) and the KAC rail fore end flip-up front sight (KAC part number 99051). The Mod 1 also uses the KAC 600 meter flip up rear (KAC part number 98474).

All first production SPRs were assembled at NSWC Crane, Indiana. The first 150 receivers utilized 18 ½ inch barrels manufactured by Krieger (50), Douglas (50) and Snider (50 polygonal). Interestingly, the initial rifles used a 20-inch barrel. When it came time to procure, the Navy would not procure a 20-inch barrel because one already existed – the 20-inch M16A2/M16A4 barrel. So a new barrel could be procured to conform with the requirements. The length was reduced to 18.5 inches and that was ok to procure due to it not already being in the inventory. The barrel would use a standard rifle length gas system. The Douglas barrels, primarily based on performance as well as cost, became the barrel of choice. These barrels were attached by an aluminum free-floating handguard to an ArmaLite flat top (M1913) rail upper receiver. Added to the upper receiver was the Swan #38 sleeve rail or Swan Sleeve. SOCOM found that the ArmaLite as well as Colt receiver was approximately .005 too tall and caused some problems. To keep parts commonality with parts available in the supply chain, SOCOM eventually went with as many existing parts in inventory as possible. There were two main triggers in use. Due to the fact the SPR would have to perform as both a sniper rifle and a light machine gun, a match grade trigger was required but also with the capability to fire fully automatic. The first trigger implemented was the Knight’s Armament Company two stage selective fire trigger and the second was Accuracy Speaks single stage trigger. Based on research, it appears that the last production rifles used the Accuracy Speaks single stage selective fire trigger group.

When the MK12 was finalized, the acronym would remain the same but what it stood for would be different. SPR originally meant Special Purpose Rifle; however now it would stand for SOF Precision Rifle or Special operations forces Precision Rifle. Within 12 months, Crane took all their gained knowledge and used it to develop 24 second generation prototypes that were more adaptable to production on a larger scale. As originally envisioned, the upper receiver was designed to be dropped into the M4A1 lower receiver. For any number of reasons, this really was not a good idea. By building a dedicated rifle, it could be designed as an accurized rifle – for instance having a match trigger installed and a longer stock that would be more comfortable than the telescopic stock of the carbine. The host weapon would be the older and outdated M16A1 rifle due to the lack of availability of the M4A1 carbine at the time and a large number of obsolete M16A1 rifles were being turned in to Crane by National Guard and Reserve Units for destruction. In order to achieve the full performance requirements of the SPR, more was needed than just a drop in upper receiver.

A: On the left is the Sierra MatchKing 77gr OTM as first used in the Mk262 Mod 0 ammunition compared to the current Mk262 Mod 1 load on the right with the addition of the cannilure. B: Ballistic gel tests of the Mk262 Mod 1 ammunition provided by Jeff Hoffman, President of Black Hills Ammunition. C. On the left is the early Mk262 Mod 0. Note the 77gr Sierra OTM projectile. On the right is the current Mk262 Mod 1. Note the addition of the cannilure to the 77gr projectile. There were several improvements made to the ammunition from its initial to current load.

In October of 2000, formal testing of the first SPR rifles began at Thunder Ranch in Texas. Combination of operational and technical experimentation showed the remaining weakness that would be corrected before the production run of the second generation SPR rifles. During winter of 2000 and 2001, all the final changes were made and deficiencies were corrected. The first 100 Limited User Test (LUT) was set for large production runs. The plans called for these LUT rifles to be deployed with SOCOM operators overseas by the summer of 2001. These initial deployments allowed the users to evaluate and make suggestions for improvement before the final production run. Most of these initial 100 rifles were called into service due to Operation Enduring Freedom in September 2001 so the field trials were conducted in just that, the field. The SPR has been used with great success with Special Operations Forces engaged in combat in Afghanistan. The SPR is responsible for an extremely high percentage of enemy soldiers engaged and killed with precision rifles. The SPR rifle was now to be named, the Mk 12. There would be two basic models of the Mk12, the Mod 0 and Mod 1.

The Mk 12 Mod 0 and Mod 1 use the same lower receiver. The M16A1 lower receiver is fitted with a selective fire match grade trigger; the Knight’s Armament 2-stage selective fire trigger or the Accuracy Speaks single action trigger. The rifle is designed as a precision shooting rifle, however if needed, with the flip of the selector, the rifle can put down a heavy volume of fire. The barrel would be done as a match barrel after heavy automatic fire but that can be easily replaced if a high volume of fire was needed to save lives. The rifles may or may not be found with the ergo-grip manufactured by Falcon Industries, or with the standard A1-style pistol grip. Many of the lower receivers will have ambidextrous selector levers as well as ambidextrous Norgon magazine catches. Once rifles got to their units/end users, they were also customized for the unit or end user. Various pistol grips may be found and also seen has been telescopic stocks on Mk12 rifles. Due to the rifle length gas system and shorter 18-inch barrel, along with the heavier profile of the barrel, it was found the Mk12 would not run reliably on full automatic with a carbine buffer but would with the standard stock and buffer. However, some felt the shorter stock was worth the tradeoff of difficulty with automatic fire. During research, photographs have been found with Mk12 rifles built on M16A2 lower receivers as well with the 5/8 of an inch longer stock.

Finalized MK12 Mod 0 rifle. Note the M16A1 lower receiver that would be equipped with a Knight’s Armament two stage selective fire trigger group. The rifle uses Precision Reflex carbon fiber free floated handguard with a A.R.M.S., Inc. Swan #38 SPR sleeve and rear sight as well. The front sight is Precision Reflex and the Harris bipod is attached via A.R.M.S. #32 bipod adapter.

The upper receivers for the SPR/Mk12 series rifles utilize the standard flat top upper receiver with feed ramp cuts for use with a barrel extension also cut with extended feed ramps. Early production rifles would use a standard M16A4 flat top upper receiver (no extended feed ramps) and the feed ramps would be cut into them with a Dremel tool. The feed ramps were necessary so the thin jacketed 77-grain MatchKing bullets would not be damaged while feeding. The upper receivers in use are mostly produced by Colt that also includes upper receivers made by Diemaco/Colt Canada. Colt purchased Diemaco May of 2005 renaming the company Colt Canada. Prior to this acquisition, Colt purchased Diemaco manufactured upper receivers for both production M4 carbines as well as spare parts.

In the development stages, three manufacturers of barrels were used and tested; these would be Douglas, Kreiger and Schneider. In final selection, the Douglas barrel was chosen for a combination of accuracy, quality and cost. The barrel is made of high quality 416 stainless steel. This barrel utilizes a 1 turn in 7 inch twist with six lands and grooves and a right hand twist. The 1/7 twist was necessary to stabilize projectiles from 77 to 100 grains (subsonic). The end of the barrel has an Ops, Inc. muzzle brake, which has threads for mounting the silencer. The silencer is made by Ops, Inc. as well. Both incorporate Harris bipods. The rifles may also be found with various sound suppressors. The muzzle brake was very effective but also very loud. Due to complaints about the loud muzzle blast a screw-on flash suppressor was designed. This makeshift flash suppressor slid over the muzzle brake and screwed onto the threads. The concept was excellent and worked well but never really made it out of the prototype stages.

Update done to the Mk12 Mod 0 rifles by Precision Reflex, Inc. in July of 2007. Note the shorter 16-inch barrel and the rail mounted front sight. The rifle has the PRI Gen III forearm and ACE M4 SOCOM stock.

Both versions of the rifle utilize the PRI made Gas Buster charging handle, which is designed to prevent any gas from the upper receiver exiting out of the rear. The Gas Buster charging handle seals the rear of the receiver so the shooter will get no gas in his face. Some operator were known to put rubber ATV around where there were gaps in the fit between the charging handle and receiver to further seal that area from escaping gas.

Both rifles utilize the same main optical sight: the Leupold TS-30A1 and the TS-30 A2. Both are a 3x to 9x variable scope. The A2 model has the option for the operator to use an illuminated reticle. The intensity of the light may be adjusted by the knob on the top rear of the scope. This was the standard optic but you will encounter numerous types of optics in use.

The MK12 Mods 0 and 1 are designed for the Ops, Inc. sound suppressor. In order to accept the suppressor, the Ops, Inc. muzzle brake and suppressor collar are installed on the barrel. On the bottom was an experimental flash suppressor attachment. It was screwed onto the muzzle brake converting the muzzle brake into a flash suppressor. Many users requested this due to the extreme muzzle flash seen with the use of the muzzle brake. It never went to production but was an excellent solution to the problem at hand.

The Mk 12, Mod 0
NSN 1005-01-504-3275

The Mk 12, Mod 0 is carried by the U.S. Army Special Forces Rangers. The Mod 0 has a weight of 11.70 pounds. The major difference in the Mod 0 and Mod 1 is the handguard assembly and the back-up sights. The Mod 0 uses the A.R.M.S., Inc. #38 SPR Mod. Swan Sleeve with the PRI (Precision Reflex Industries) Ged III Freefloat Forearm, which is made from aluminum and carbon fiber materials. The Swan Sleeve goes from the handguard and covers and protects the rail on the upper receiver. At the rear of the rail is the SWAN #40 Stand Alone Flip-Up rear sight. The gas block is made by PRI and has a folding front sight. The front sight post is adjusted for elevation by a dial on the front sight assembly. If the optic was lost, by turning the two throw levers on the scope mount, the scope can be removed and both back-up sights can be engaged and the rifle will be ready for action.

The optics (light sources, bipod, etc.) are attached by A.R.M.S., Inc. throw lever mounts that allow for quick detachment if there is an immediate need to go to iron sights. For scopes, the throw lever mount #22M is used. Both Harris bipods as well as Versa-Pods are used. The upper receiver provided for this article was one of David Dunlap’s original uppers he built towards the beginning of the project. David Dunlap is the President of Precision Reflex, Inc.

The front sight base of the MK12 Mod 0 contains a folding front sight that is adjustable for elevation only.

In July of 2007, Precision Reflex, Inc. rebuilt 12 Mk12 Mod 0 rifles at Fort Campbell, Kentucky. These rifles deviated from the standard Mod 0 in 8 ways:

Replaced the barrels and bolts with a 16” Douglas, 1:8 twist 5.56 barrel – PRI #06-681BB
Removed the barrel mounted front sight with a PRI Rail Mounted Flip Up Front Sight – PRI #05-0028
Added a new gas block with intermediate length gas tube – PRI #05-075-01
Replaced the forearm with a new PRI Gen III Rifle Length Forearm – PRI #05-073-03
Replaced the old OPS Brake and sleeve with a New Ops Brake and Sleeve
Added a new ACE M4 SOCOM stock
Added an Accuracy Speaks full auto trigger
Replaced the Old PRI Gas Buster Charging Handle with new PRI Gas Busters – PRI #05-0031. (Old ones quickly “disappeared” to other users)

The rear sight for the MK12 Mod 0 is the A.R.M.S., Inc. #40 backup sight that has both long and short range apertures and is adjustable for windage only. RIGHT: The Mod 1 also uses the KAC 600 meter flip up rear (KAC part number 98474), which is adjustable for windage only. OPPOSITE PAGE TOP: The Mod 1 uses the KAC rail fore end flip-up front sight (KAC part number 99051) which is adjustable for elevation only.

The Mk 12, Mod 1
NSN 1005-01-504-3276

The Mk 12, Mod 1 is carried by U.S. Army Rangers, U.S. Navy SEALS and the U.S. Air Force Special Tactical Teams. The Mod 1 has a weight of 10.80 pounds and uses many of Knight’s Armament Company’s (KAC) components. The Mod 1 uses the KAC Free Floating RAS (Rail Adapter System) that has full length quad Mil-Std 1913 rails. This rail system does not use a sleeve like the Mod 0. Optics would be mounted right to the upper receiver or the rails on the Free Floating RAS. The KAC folding back-up sight is used on the rear of the upper receiver rail and a folding front sight is used. The gas block is made at Crane. The Mod 1 uses A.R.M.S. #22 High scope rings that attach right to the rail. The Mk12 Mod 1 upper receiver used during the research of this article was provided by Lamont LeClair, active duty SEAL and owner of Centurion Arms. Monty was able to provide much insight to how the Mk12 is used and what it really brings to the table for SOF units.

The New Improved SOCOM 5.56x45mm Cartridge

In 1999, SOCOM requested that Black Hills work with them jointly to develop the MK12 Special Purpose Rifle (SPR) weapon system. SOCOM was to develop the rifle and Black Hills Ammunition was to develop the ammunition the new rifle would shoot. This rifle was to be accurate out to 600 yards. The load would use the proven Sierra 77-grain open tip match projectile of the AMU. To meet the requirements the cartridge must be “militarized.” This included switching from .223 Rem. to 5.56mm cartridge cases, loading to the increased 5.56mm pressures, crimping and sealing the primers and adding flash retardant to the powder blend. Black Hills Ammunition has developed the first 5.56mm sniper cartridge, the MK262 Mod 0 cartridge adopted in 2002.

During evaluation of the new round, issues came up with reliability when the temperatures dropped and the guns got dirty (external dirt, not ammunition). Issues with short stroking when the rifles were in these conditions without sound suppressors were encountered in the cold with the SPR, which uses a 2 inch shorter barrel than the original 20-inch M16A2 gas system the SPR was built on. Black Hills got right on the problems and through switching to a slower burning powder with a pressure curve tweaked for the 18-inch SPR barrel, the MK262 Mod 1 was born. Later during extremely rigorous function testing at Black Hills, when the weapons were fired at rates greatly exceeding the 12 to 15 round spec rate of fire for the M16/M4 weapon system, it was found that the new propellant was more sensitive to heat from the chambers of hot weapons. This resulted in the increased pressure and increase incidences of failure to extract. Black Hills notified NSWC-Crane and set out to work again to improve the load. By working on a powder blend with higher heat tolerance and improving the brass, these issues were overcome. Another issue that needed to be addressed during the product improvement was Black Hills desire to have Sierra manufacture a cannulure on the 77-grain OTM projectile. Sierra feared this would affect the accuracy of the projectile. Black Hills knew that this round is being used in an autoloading rifle and wanted to avoid the possibility that a rough feed could cause the bullet to push back or telescope back into the case, resulting in a malfunction. Sierra agreed to produce the cannilured version of the projectile. The new and final round was named the MK262 Mod 1 in 2003 and with the correction of the temperature sensitive powder the specification changed but remained the Mod 1.

The Mk262 Mod 1 has gone on to be the most sought out ammunition in the 5.56mm line up for the U.S. military. Primarily used Mk12 SPRs, it has also proven to increase the accuracy and lethality of the 14.5 inch M4 as well as the Mk18 CQB with a 10.5 inch barrel. This author has shot a Mk12 Mod 1 at a silhouette steel target at 850 yards consistently, which is way out of the range of a standard 5.56mm/.223 Rem. caliber rifles and ammunition. The combination of rifle and ammunition has served admirably in both Iraq and Afghanistan. Special operations troops have great confidence and there is an interest in clones of this rifle in the commercial market. For someone looking to build a Mod 1, Centurion Arms offers a complete upper receiver down to the last detail including a Douglas barrel. If one wished for a Mod 0, the upper receivers are built and sold by Precision Reflex, Inc.

Issue box of the highly regarded Mk262 Mod 1 ammunition that was designed with the Mk12 SPR.

Rugged, Ergonomic Design and Simple Function

The shortened optical length and large objective of the MRO virtually eliminates the tube effect. With 5 years of continuous use on a single 2032 battery, the dot is bright, crisp and always visible when you need it! The MRO is parallax free with infinite eye relief for quick and accurate engagement no matter your position. Half-minute adjustments with 70 MOA available allow for zeroing in most any configuration on numerous weapons with no special tools required. The MRO features eight brightness settings, including two that are night vision compatible and one extremely bright setting for use with lights or in bright outdoor conditions. Placing the adjustment knob on top keeps things ambidextrous. With a 2MOA dot you get fast target acquisition up close without washing out or losing the target at longer ranges. Tested to operate in temperatures ranging from -60F to +160F, the MRO covers the world! Waterproof to 100 feet, chemical and corrosion resistant, and housed in 7075-T6 Aluminum it is built to withstand the harshest combat or duty conditions.

From CQB distances to the limits of the 5.56mm cartridge, the MRO delivers a compact, light, and rugged aiming solution. Learning from years of RDS use in combat and Law Enforcement, along with input from operators around the world, the MRO takes combat RDS sighting to the next level. The sense of looking through a tube or tunnel is all but eliminated. The glass is clear, the dot crisp, and the overall size about perfect. Zeroing is easy with no special tools required for adjustment – even a 5.56mm casing will work. Snap your rifle into the pocket and the dot is just there, no tunnel, no searching, just a dot and your threat, satisfying the needs of just about any real-world operator.

Trijicon has once again taken the science of the red dot sight to the next level. Built to withstand the rigors of combat, or the mean streets of law enforcement, the Trijicon MRO sets the standard. Light, rugged, easy to use, mount and zero, with extended battery life and a clear field of view it does everything you can ask of a red dot sight. Trijicon’s proven track record ensures longevity, dependability, and usability in the real world. If you are looking for the best, then look no further than the Trijicon MRO!

The MRO is a self-contained, disposable, single-shot 72.5 mm rocket launcher, developed from the larger 93 mm RPO family to provide a lighter alternative. Both the MRO and RPO series weapons have descriptions translated from Russian as “flamethrowers,” referencing the three incendiary-type warhead variants produced.

The MRO-A,pictured in, carries a thermobaric warhead and is distinguishable by the two short red stripes towards the firing end of the weapon. The MRO-D variant carries a white phosphorous (WP) smoke warhead, identifiable by one red stripe, and the MRO-Z an incendiary warhead, marked by a single yellow stripe. The RPO series is available in the same variants, featuring the same markings and designations.

The presence of the MRO in Ukraine was significant because, unlike the RPO, it is not known to be in the Ukrainian military arsenal. As seen, a cache of RPO-A launchers was allegedly captured from pro-Russian separatists following fighting at the Donetsk airport. In late January 2014, Pravda News also reported a request Vitaly Zakharchenko, then Ukrainian Interior Minister, asking for permission to use the RPO-A to “help maintain public order and public safety.”

Special thanks to Ivan Kochin and Yuri Lyamin for their assistance.

Technical Specifications:

MRO series:
Calibre: 72.5 mm
Length: 900 mm
Weight: 4.7 kg
Effective Range: 90 m
Maximum Range: 450 m
Variants: MRO-A (Thermobaric warhead), MRO-D (WP Smoke warhead), MRO-Z (Incendiary warhead)

RPO series:
Calibre: 93 mm
Length: 920 mm
Weight: 11 kg
Effective Range: 200 m
Maximum Range: 1000 m
Variants: RPO-A (Thermobaric warhead), RPO-D (WP Smoke warhead), RPO-Z (Incendiary warhead)