ABOVE: Windham Weaponry MCS

The M16/M4 weapon system entered a new era in 2003 and would redefine the term “modular rifle”. In 2003, Lewis Machine & Tool introduced their MRP or Monolithic Rail Platform. This one piece receiver has user level interchangeable barrels. By removing two bolts, the barrel was pulled from the receiver and the user could swap out barrel lengths, operating systems and different calibers. In 2005 another modular carbine was introduced by MGI’s Mack Gwinn, called the Hydra rifle. In concept it was similar to the MRP in the fact you have removable barrels but where it departs is in the lower receiver.

The new weapon system Mack came up with was one unlike ever seen before in the history of the AR family of weapons. Up until the 2002/2003 time period the AR was basically 5.56mm only. None of the wonder calibers really made their premier until much later. The other calibers that did gain traction at the time were the 7.62x39mm and 9x19mm. The platforms were the basic dedicated AR-type upper receiver put on with a conventional barrel nut. The 7.62x39mm variation was problematic. The reason being is the magazine well. The heavy taper on the 7.62x39mm cartridge case caused the cartridges in the stack to form the ever popular “banana” shape. This is why the AK magazine has such a curve to it. When you try to stack a tapered case as such in a straight line as what is required with the straight AR magazine well, there are failures to feed. Several companies tackled not only building an AR rifle chambered in the popular Soviet caliber but they also tried to develop a magazine which would work as well. It really was not successful in releasing a reliable feeding platform. This was not due to the functioning but due to feeding problems caused by the magazine. In the early 1990’s, Colt introduced their Sporter Target rifle chambered in 7.62x39mm. They introduced this as a potential hunting rifle for medium sized game. They had modified 20 round magazines that only fed 5 or 6 rounds reliably. Some aftermarket companies introduced 30 round mags but they suffered from reliability issues. Colt would later take this rifle off the market due to reliability issues. The first company to successfully combat this feeding issue only produced 6 rifles for Special Operations as proof of concept. Knight’s Armament developed the SR47 on 2001 at request of Special Operations. It was an M4-type rifle that used an AK magazine. Unfortunately they never went into production. This would be on the mind of Mack in designing the Hydra.

The 9mm AR was first introduced by Colt in the 1980’s. To make everything work as reliably as it did required a two part magazine well insert. The front insert provided the feed ramp and the rear had the modified fixed ejector and modified bolt catch to work with the UZI pattern magazine. In fact the magazines were originally modified UZI mags. This required drilling holes to pin the inserts in place. One would not want to remove these adapters to convert back to 5.56mm. The constant removal and reinstallation would damage the receiver. This was a robust system. In the 1990’s, Colt’s Arthur Daigle designed a one piece mag well adapter. It was removable. By rotating a hexbolt, two arms would extend out of the assembly and lock it inside the magazine well.

Unfortunately, people could not grasp how tight to torque the bolt, they would over torque and the arms would bend the magazine well outward damaging the mag well. So Colt modified the one piece magazine well adapter and pinned it in place. The lower became a dedicated lower receiver. This would also be on the mind of Mack during his development of the Hydra.

Mack thought, what if I had a modular lower receiver that would correct the issues with making a reliable 7.62x39mm AR platform rifle as well as an easily convertible 9mm? Thus came the Hydra. The Hydra lower receiver has removable magazine wells enabling a single lower receiver to accept different magazines. By disengaging the trigger guard and pressing the magazine release button the magazine well is lifted off of the lower receiver. What does this do? Well it enables a 9mm mag well to be installed permitting use of Colt Pattern 9mm magazines. By having this modified 9mm magazine well, this was all the lower needed to accept a 9mm barrel to reliably fire 9x19mm ammo. This magazine well was tested with ASC, CProducts Defense as well as Metalform magazines with 100% compatibility.

Without doubt, the most impressive of all, there is a magazine which accepts AK-pattern magazines. Mack knew the only way to make the 7.62x39mm reliable was to use the proper tried and true magazine. This magazine well adapter lacks the bolt catch due to the AK magazine not having a provision to actuate it. The magazine release is also rather ingenious. There is no latch in front of the trigger like an AK. It is a button just like the standard AR. There is an angled bolt/magazine catch that engages the locking tab on the rear of the magazine. As the magazine is inserted the tab engages that angled part and pushes the mag catch outward allowing the magazine to be fully inserted. Once fully inserted the mag catch engages holding the magazine in place. This works very well with steel AK magazines. However the inconsistence of the latch on the polymer magazines makes polymer magazines hit and miss if they will work/seat. The Soviet and Chinese Bakelite magazines have steel locking tabs so they work perfectly. The polymer tabs often can be too thick. With a file they can be taken down just enough so they will engage the magazine release. The steel angled bolt can also wear the polymer tab prematurely. Stick with military grade steel and Bakelite magazines you will never go wrong. However, the Magpul MOE/ Gen 3, US Palm and Bulgarian magazines work perfectly. The bolt carrier group for the 7.62x39mm has been modified as well by Windham Weaponry. The bolt carrier is stamped 7.62 on the left side. The bottom of the carrier has had some extra relief cuts on the bottom to accept the slightly higher AK magazine. However, if one should decide to use the AR15 magazine well adapter and use AR-pattern 7.62x39mm magazines, these relief cuts will not affect reliability. The bolt is modified for the 7.62x39mm cartridge case and is identified by 3 rings just behind the locking lugs by Windham Weaponry to differentiate quickly between the 5.56mm bolt. The firing pin is slightly heavier as well to be able to reliably fire the harder military primers of the Russian and foreign military ammunition.

Of course Mack designed a standard AR magwell as well. This would accept any 5.56mm magazine. Just around the time the Hydra premiered, two new calibers were to hit the market. These were the 6.5 Grendel as well as the 6.8mm Rem SPC cartridge. These would use a modified version of the standard 5.56mm magazine. So this immediately made the Hydra compatible. It also enabled the rifle to take the not so reliable 7.62x39mm AR-pattern magazines if the user was so inclined to venture in that direction. During testing of this Windham Weaponry MCS rifle, numerous magazines were tested for compatibility. These included GI aluminum, Magpul PMag, Lancer AWM, Ultimag, Hera Arms, Amend 2, H&K steel and polymer, Surefire 60 round, Hexmag and X-Products 50 round drum to name a few were tested for compatibility. There were no issues at all.

So now Mack had the lower receiver squared away for the three most popular calibers for the black rifle. Now how to make the upper just as modular as the lower? The upper receiver is also extremely unique. Unlike other models, the Hydra does not require a proprietary barrel for its removable barrel system. The Hydra uses a standard barrel with a standard barrel extension minus the delta ring, spring weld and snap ring. The barrel has the gas block installed with the standard carbine length gas tube pinned in place. The barrel slides into the upper receiver and indexes off of the pin on the receiver extension. Once in place there are two locking levers that rotate and lock the barrel nut into the upper receiver. Once the two locking arms are in the locked position a retaining block slides up the Mil-Std-1913 rail covering the locking arms holding them in place. Then a safety bail snaps in place to hold it in position. Now to be able to use the AK magazines, some modifications had to be made to the inside of the upper receiver that would not affect the function of the other calibers. The upper has the forward assist, fired cartridge case deflector as well as the ejection port dust cover.

In late 2015, Mack (MGI) had decided two things. First they did not have the distribution network to meet the potential of their Hydra Rifle. Second, they are a small company and have never been able to ramp up production to meet the demand of the Hydra rifle. It would make sense for them to partner up with an established AR manufacturer who had both a large distribution network, marketing resources as well as a production capacity to move the weapon system forward to meet the demand. They came to a licensing agreement with Windham Weaponry for them use the technology under the Windham Weaponry MCS designation. At SHOT Show 2016, Windham Weaponry introduced their MCS or Modular Carbine System. They offer four different configurations. They offer 5.56mm (.223 Rem), 300 Blackout, 7.62x39mm and 9x19mm calibers. They offer three packages. The first is the RMCS2 which is the MCS rifle with the AR15 magazine well and two barrels. One chambered in 5.56x45mm and the other in 300 Blackout. Each kit comes with a Plano Gun Guard case. The next is the RMCS3 which is MCS rifle with the AR15 magazine well adapter as well as the AK magazine well adapter. There are three barrels chambered in 5.56x45mm, 300 Blackout as well as 7.62x39mm. The RMCS4 which is a MCS rifle with the AR15 magazine well adapter , AK magazine well adapter and 9mm magazine well adapter. There are four barrels chambered in 5.56x45mm, 300 Blackout, 7.62x39mm and 9x19mm.

The kit was provided with a Windham Weaponry 30 round 5.56mm/300 Blackout magazine, a 30 round Magpul MOE AK polymer magazine and a ASC 20 round 9mm magazine. With the kit was also a sling and a SafeTech SAFE-T-ROUND chamber plug which comes in the chamber of the MCS rifle. There are three supplied modular magazine wells provided which are the standard AR15, AK magazine 7.62x39mm and 9x19mm. Fit and finish of all the components was top rate. Added by the author are the ARMS #40L rear sight to the receiver and the three barrels (5.56x45mm, 7.62x39mm barrel and 300 Blackout) had the ARMS #40-LF front sight bases added to the gas blocks.

The Windham Weaponry MCS RMCS4 test and evaluation kit was provided with four barrels. The barrels chambered in 5.56x45mm, 300 Blackout and 7.62x39mm barrels are standard manganese phosphate and chrome plated barrels. All barrels have the barrel extension and A2-compensators. The front sight base has a bayonet lug and sling swivel. Top of the gas tube has a Mil-Std-1913 rail which is aligned with the rail on the upper receiver/handguard. The front sight base is drilled and pinned in place which is preferred by this author. They all have carbine length gas tubes installed. The 5.56x45mm barrel has 1/9 inch twist, the 300 Blackout has a 1/7 and the 7.62x39mm has a 1/9.5 inch twist. The 9x19mm is Melonite coated with a 1/10 inch twist and birdcage flash suppressor. There is no gas block on the 9mm barrel.

The first barrel tested was the 7.62x39mm. Ammunition tested was Federal American Eagle 124gr ammunition (100 rounds) , Hornady 123gr SST (50 rounds) and Wolf 122gr full metal jacket (200 rounds). There were no malfunctions of any sort. The magazines used were Russian and Eastern European steel AK mags, Magpul MOE and Gen 3, US Palm and Soviet Bakelite. The best group was obtained with the Hornady SST ammo with 1.75 inch group at 100 yards.

The second barrel tested was the 300 Blackout. The standard AR modular magazine well was used. Ammunition was Black Hills 300 Whisper 125gr OTM (200 rounds), Barnes 110gr TAC-TX (100 rounds) and Hornady 110gr VMAX (100). The magazine tested were the Windham Weaponry aluminum, PMag Gen 3, Lancer AWM, Ultimag and Amend 2. No malfunctions of any sort. Also Remington 220 grain OTM (20 rounds) was tested. Numerous short strokes were experienced but this is to be expected when a sound suppressor is not being used. The best group was with the Black Hills 125gr OTM with 1.35 inches at 100 yards.

The third barrel tested was the 5.56x45mm. The standard AR modular magazine well was used. Ammunition tested was Black Hills .223 Rem 55gr FMJ (100 rounds), Black Hills 5.56x45mm 69gr OTM (20 rounds), ZQI 5.56mm 62gr full metal jacket (100 rounds) and HSM 5.56mm 62gr full metal jacket (100 rounds). The magazines tested were the Windham Weaponry aluminum, PMag Gen 3, Lancer AWM, Ultimag and Amend 2. No malfunctions of any sort. The best group was obtained with the Black Hills Match 69gr with a just over 1.25 inch group at 100 yards.

Lastly the 9x19mm barrel was tested. The modular 9mm magazine well was used. The ammunition was Black Hills 9mm Luger 115gr full metal jacket (200 rounds) and Federal American Eagle 9mm 147gr full metal jacket flat point (100 rounds). The magazines uses was the 20 round ASC magazine that came with the kit as well as two of the Metalform 32 round Colt magazines. There were no malfunctions of any sort. This set up was fired at 25 yards. Best group was with the Black Hills 115gr full metal jacket at 1 and 1/2 inches. It was hard to pick the best group between the Black Hills and Federal ammo since they were nearly identical. For someone who chooses to fire a significant amount of 9mm through the MCS, it would be advisable to put a 9mm SMG buffer and to change out the hammer pin with a stainless steel one. These are two improvements that would benefit you for long term use of this caliber. For occasional the standard buffer will work just fine. MGI also offers a Heavy Rate and Recoil Reducing Buffer which also work well to alleviate the stress on the rifle from the 9mm operating dynamics.

The Windham Weaponry MCS is truly in a class of its own. With this industry growing as rapidly as it is the licensing agreements between MGI and Windham Weaponry will surely increase the demand and popularity of this weapon system and be able to meet this demand with production efforts. Many companies have gone the interchangeable barrel rout over these intervening years. But nobody uses standard barrels. They use proprietary systems. Also, nobody has come up with the modularity of interchangeable magazine wells. There is a lot to be said about using factory standard components. For the manufacturers of these weapons, it makes production much simpler. Looking at the MCS, really the only proprietary components are the barrel locking mechanism and the lower receiver/ magazine wells themselves. All the components that go into the magazine well assemblies (minus the 7.62x39mm) are all industry standard, the fire control group and recoil system and stock assemblies are factory standard. The charging handle and bolt carrier groups are factory standard (minus 7.62x39mm carrier and firing pin). The barrel assemblies are completely standard. As more calibers come out the MCS will be able to adapt. This is a true one rifle can do it all. Now is this a military grade weapon? That has yet to be seen. For a gun enthusiast and shooter it is certainly adequate for that and according to Windham Weaponry the components wear on this rifle at the same rate as a standard M4. MGI still continues to sell their Hydra and design and manufacturing new upgrades and barrel kits. Only time will tell how successful this will be but it is certainly moving in the right direction to see the rifle live up to its potential.