The U.S. Marine Corps' New M27 IAR: Part One

The U.S. Marine Corps’ New M27 IAR: Part One

21 November 2011, The Crucible training center, Stafford County, Virginia. Big and little brothers. The USMC’s new M27 Infantry Automatic Rifle is a lightly modified version of Heckler & Koch’s HK416, seen here with a compact 10.4 inch barrel. HK’s M27, supported by its Harris/LaRue bipod and topped with the Trijicon 3.5 power TA11SDO-CP, is equipped with accessory items that will be standard in USMC service including black colored synthetic rubber Manta rail and broomstick covers. (Robert Bruce)

Reidsma:  We have to meet the USMC’s specifications.  For the initial RFI (Request for Information) in 2005, we looked back at our XM8 or G36 type systems and we also looked at the 416 or possibly doing something else.  When it came down to the actual specs in the requirement we said ‘416 should meet the requirement.’  A true commercial-off-the-shelf system that was ready at the time. The HK416 has a similar appearance and operator training as the current M16A4 and M4.  Incorporate and integrate the ancillary items that meet the Marine Corps requirements and other specified items and then submitted the HK416 as our version of the IAR.

When it comes to open bolt vs. closed bolt, a closed bolt system is going to be more accurate compared to an open bolt, so it’s a tradeoff.  In order to meet the accuracy requirement we put our effort towards a closed bolt system because we knew we could get the accuracy out of it.  So far this accuracy appears to average about 2-3 minutes of angle with a 5-round group using M855 ammunition.  A benefit of the HK416/M27 IAR gas piston – operating rod style of operation is that there is a reduced amount of heat going back into the chamber and bolt group which allows for a sustained rate of fire higher than the M16/M4 direct gas operating systems.

SADJ:  How about not exclusively closed or open bolt, but a switchable system? 

Reidsma:  With our gas piston system, the majority of the heat is located in the gas block area of the weapon so it is away from the chamber.  Roughly 90 percent of the hot gas and carbon exits through the muzzle of the barrel and gas block.  This allows enough of a time/distance ratio before the chamber gets too hot.  It’s a “heat sink” that gives you enough time to get to at least the minimum sustained rate of fire specified under the conditions.  The HK416/M27 IAR is a simple, more reliable system; closed bolt system for accuracy and the gas piston operation allows for the sustained rate of fire the Marine Corps asked for.  A switchable system could be developed, but would add cost and time, and would need to be thoroughly tested for reliability, which is not always available or desirable under acquisition timelines and fiscal resources.

SADJ:  Belt fed vs. magazines remains an open question.  You can slam an M16 mag in the side of a SAW.

Reidsma:  You can, but there’s a reliability question with the M249 and magazines.  The machine gun technical and operator manuals will tell you there are reliability issues when you put a magazine into the SAW.  The Marine Corps’ requirement said the IAR had to work with the US government 30 round magazine.  It all goes back to the role and use of an automatic rifle within the infantry team and squad compared to that of a belt fed, open bolt, light machine gun.

21 November 2011, The Crucible training center, Stafford County, Virginia. HK’s Robbie Reidsma (left) with an M27, and Trijicon’s Jimmy White with an HK416 10.4 inch barrel version, inspect a silhouette target showing the results of some of the morning’s CQB practice. (Robert Bruce)

SADJ:  What performance and other factors led to the decision to adopt HK’s modified 416 rifle as the USMC’s Infantry Automatic Rifle?

Reidsma:  This is more of a USMC question.  HK’s IAR met the requirements.

SADJ:  Comment on HK’s assertion in a recent press release that their entry was “Developed at no cost to the U.S. taxpayer….”  HK wasn‘t paid to respond to the solicitation, to deliver samples, to be there during the testing, for spare parts if needed and these sorts of things along the way?

Reidsma:  It’s a true ‘non-developmental, commercial-off-the-shelf’ gun.  A good, reliable system, already developed internal to HK based on previous requirements that HK took on board themselves. Yes, as with the other companies’ systems per the contract, samples and spare parts were purchased and delivered for testing, however no government R&D dollars were spent.

SADJ:  What ‘lessons learned‘ in formal tests, field evaluations, combat experience, etc. have resulted in engineering or other modifications to the M27?

Reidsma:  Most of these came from the users during the limited fielding portion; the two point sling, rail covers and bipod were upgrades to the system.  Other than ancillary type gear there’s really no major changes with the gun.  More of the ‘creature comforts’ that allowed better marksmanship such as the sling or better employment of the system such as the bipod and rail covers.  It goes back to newer “stuff” vs. older “stuff” with modifications.

M27, disassembled.

SADJ:  The Marine Corps tells us that hot weather testing showed the desirability of slowing the cyclic rate a bit with a slightly larger exhaust port in the gas block.  Other than that, were there engineering changes?

Reidsma:  As far as the gun goes, it’s the HK416 system, the same thing.  We did slightly adjust the gas block exhaust to further improve long term durability of the system in a range of environments and to better coincide with the intended use of the IAR and government ammunition.  Most of the improvements were new developments at the time.   You saw the firing pin retaining pin being round and captive and the reversible charging handle.  Those were the new developments at HK at the time.  Where now it‘s kind of a standard build or an additional accessory in a regular production run.  We incorporated those developments into the M27 system.  But as far as ‘do we have to change the operating system or do we have to change components or materials or something like that along the way?’ the answer is really no.  No magic, no HK witch doctor, nothing complicated (laughs).  It’s a commercial-off-the-shelf gun.  And the cold hammer forged barrels last for fifteen thousand rounds, even with a lot of full auto fire.

SADJ:  We’ve asked the Marine Corps for their comparison of M27 vs. M249 as far as cyclic rate, sustained fire, range, accuracy, reliability, ease of handling, etc.  Your comments?

Reidsma:  Cyclic rate is about 700 to 900 rounds per minute.  This is about the same as the M249.  Sustained rate of fire is approximately 36 rounds per minute or three times that of an M16 and almost that of the M249 SAW sustained rate of fire of 50 RPM.  In a comparison – and you have to look at how the system’s being used and employed – the sustained rate of fire of 36 rounds per minute is what we’ll say it will do.  It can actually do better than that.  Because it is a closed bolt to get the accuracy, the ambient temperature can play a role.  As your ambient temperature decreases from 120 degrees you can actually get a higher sustained rate of fire out of the system.

When it comes to the range, we’ll list a ‘graduated range’ so it’s what the sighting system will do along with the ammunition.  So if you’re using the SDO (Squad Day Optic) it will go out to a thousand meters; if you’re using the iron sights it’s out to six hundred.  You can shoot the rifle out to six hundred, no problem at all and you can hit point targets with it.  You can get area fire on a group of targets out to a thousand meters.  Compared to the SAW it’s the same thing.  Compared to an M16A4, the M27 is a little bit further reaching due to the increased accuracy.

Reliability; fifteen thousand rounds barrel life and major components.  It’ll go beyond that but that’s what we’re guaranteeing as a minimum.  Ten thousand rounds on minor items.  One of the test process items we do is an endurance test with every lot of M27s we deliver to the Marine Corps.  The government will pick one of the guns and we’ll shoot fifteen thousand rounds the way they want it fired.  We make sure we’ve still got the accuracy and the gun still functions and is reliable as required.

21 November 2011, The Crucible training center, Stafford County, Virginia. In his introduction briefing for the live fire demonstration, Reidsma slides off the M27’s one-piece quad rail to reveal the rifle’s piston driven operating rod, a key factor in reliability and durability of the system. (Robert Bruce)

Like you saw today it’s very easy to handle.  Easy to control in burst fire.  It’s incredibly accurate like you saw today at the range when we were shooting at three hundred yards and hitting the target on the eight inch head plate.  And the rifle we were shooting has over fifteen thousand rounds through it.

When you do a comparison of the M249 and the M27, one can shoot just as fast as the other so if you really had to shoot six hundred rounds in about two or two and a half minutes you can.  But (smiles) I’d be calling for air support by that point in time.

SADJ:  Comment on the choice of Trijicon’s SDO as primary sighting device.

Reidsma:  The Trijicon Squad Day Optic is what was already on the Marine Corps’ M249s.  So that sighting system actually ended up working just fine on the M27 IAR.  It’s one of their assigned optics:  ‘The SDO will be on the M27.’  From my experience, I actually like the SDO over the Rifle Combat Optic because it does have the extended eye relief in there so it’s a lot faster to get on target.  When you’re talking about an automatic rifle on the move – more a Marine Corps tactical topic – with that system your target acquisition is so fast.  Your probability of first round hits is incredibly high and that’s exactly what you want as an infantryman closing with the enemy.  It comes down to the gun being accurate, lightweight, being able to deliver a higher rate of fire, and the optical system on it with regards to finding the threat, and then being able to transition to engaging that threat.  It’s incredibly fast through the process.

SADJ:  Comment on alternatives to standard-issue 30 round magazines to feed the M27.  Things like the C-Mag, multiple 30s clipped together, etc.

Reidsma:  It’s specified that the IAR has to work with the standard issue magazines the Marine Corps fields.  At HK we’ve done some informal evaluations of various high capacity magazines.  You saw us using some of these today in the live fire.  But it will be up to the Marine Corps to decide if they want something else.

SADJ:  Comment on how easy or difficult it has been to integrate the M27.  Things like training of operators and armorers, logistical support, changes in tactical doctrine.

Reidsma:  The M27 IAR itself is like an M16A4.  The operator ergonomics behind it; the control levers and everything, are basically the same as what’s on an M16A4.  So your basic infantry training, your qualification on the range going back to 500 yards.  All those techniques and operator ergonomics with the M27 IAR remains the same as far as how you use it, how you work the system, and how it’s fired.  So from an operator’s standpoint it’s as simple as put down one gun, pick up the other gun and go.  Simple as that.  Muscle memory is already there, training is already there, it reinforces either system, no problem at all that I am aware of.  From the operators and armorers standpoint, the way the gun works is essentially very similar.  The big difference is the gas piston with the pusher rod in the M27 IAR.  You saw today on the range it’s very easy to take apart and put together.