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Windham Weaponry's MCS Rifle System: Best Bug-Out Rifle?

Windham Weaponry's Bug-Out Bag System provides three popular calibers in one multi-caliber platform, all stored neatly, along with a small survival kit, in a backpack.

Windham Weaponry's MCS Rifle System: Best Bug-Out Rifle?

[EDITOR’S NOTE: Hydra Weaponry (formerly MGI) has taken back their rifle design from Windham Weaponry and are offering it today. They can be reached via the Hydra Weaponry Website. Windham Weaponry no longer sells the MCS Bug Out Bag system.]

What is the ultimate bug-out or survival rifle? Ask that question to 10 preppers, and you’re sure to get 10 different answers. Back in the hey-days of the 1980s, and the old “survivalist” movement, it was pretty well accepted that any prepared individual needed to have a battery of firearms to perform a variety of different tasks. Typically this consisted of a semi-automatic 7.62x51mm or 5.56x45mm fighting rifle for self-protection, a .308 Win bolt-action hunting rifle for taking big game, a pump-action 12-gauge shotgun for hunting and self-protection, and a .22 LR rifle for small game. You’ll note all perform specific rolls while chambering the most common and readily available ammunition of the time. It’s still a well thought out list even decades later.

One downside to the “traditional four” survivalist long guns is simply that it consists of four different firearms. What if you could replace the three rifles with one “do-it-all” piece? You would have less to carry, to maintain and to store. Well, Windham Firearms offers something along these lines with its MCS Multi-Caliber System. This consists of one basic AR-15-type platform, which has the ability to quickly change barrels, calibers, and even magazine wells. This allows it to swap to almost any caliber capable of being chambered in an AR-15. For example, you can easily swap from 5.56x45mm feeding from standard AR mags, to 7.62x39mm feeding from AK-pattern mags, to 9x19mm feeding from Colt-pattern submachine gun mags, and many others, no tools required. This design also allows you to quickly change barrel length. So, you can easily swap from a 16-inch to a shorter 10.5-inch barrel based upon your needs. Barrel changes take less than a minute, again. no tools required.

Windham Weaponry’s Bug-Out Bag System provides three popular calibers in one multi-caliber platform, all stored neatly, along with a small survival kit, in a backpack. Windham Weaponry’s MCS Bug-Out Bag puts a 5.56x45mm, 9x19mm and .22 LR all into an easily carried and stored system. Windham even throws in some survival gear.

While multi-caliber systems hold a certain appeal, they traditionally have a number of drawbacks. Multi-caliber typically means proprietary. Proprietary typically means expensive, limited production and hard to find. Perhaps the best example of this is Bushmaster’s ACR or Adaptive Combat Rifle. Although introduced years ago, long-promised caliber conversions for the ACR are only now hitting the market in quantity. The good news? Windham Weaponry’s MCS utilizes standard off-the-shelf barrels, bolts and parts. So any standard AR-15 barrel, bolt, bolt carrier, buffer, fire-control group, etc. will fit. You are by no means limited to what Windham Weaponry offers.

Another typical downside to brand-new multi-caliber systems is possible teething problems that need to be sorted out. These may be little or big unforeseen
problems which crop up when a firearm is newly released. Another plus for the MCS is it’s not really new. The heart of the gun is standard AR-15. The proprietary aspect of the design is well-proven over years of use. I’m sure many sharp-eyed readers will recognize the MCS as a rebranded MGI Hydra, which has been around for quite some time. The difference being MGI was a small shop with limited resources, while Windham Weaponry is a much larger company with much deeper pockets and capacity. Currently, Windham Weaponry offers the MCS in a number of different packages. These allow you to buy the host rifle and a number of different caliber barrels with the associated bolts and magazine wells required by each. For this review, I chose its Bug-Out Bag System which, as its name implies, comes in a handy backpack. This allows you to fire three different calibers, 5.56x45mm, 9x19mm and .22 LR. Inside the backpack you’ll find:

  • RMCS Lower Receiver with 5.56x45mm and 9x19mm interchangeable magazine wells
  • RMCS Upper Receiver with fixed Quad Rail Fore-end and barrel locking mechanism
  • Two barrels: 16-inch 5.56x45mm M4 Profile and a 16-inch 9x19mm
  • 5.56x45mm bolt carrier and 9x19mm blowback bolt
  • 5.56x45mm buffer and 9x19mm buffer
  • CMMG .22LR conversion kit (used with 5.56x45mm barrel)
  • Magazines: One 30-round 5.56x45mm STANAG pattern, one 20-round 9x19mm Colt pattern and one 25-round .22 LR
  • Includes: Compartmented Backpack with pouches for all components constructed of Lightweight Nylon Shell and 500 Denier Nylon interior
  • Space Blanket, Frontier Straw Water Filtration Kit, Sewing Kit, Fishing Kit, and Fire Starter Kit
  • Windham Weaponry Transferable Lifetime Warranty

I found everything neatly separated and stored once I opened the pack. The whole kit is fairly impressive. After examining the system, I began by assembling it as a 5.56x45mm rifle. At first glance, the upper receiver assembly appears to be a traditional flattop design. It features a dustcover, forward assist and brass deflector. But if you look more closely, you’ll note the very front is markedly different and incorporates two locking levers. A free-floating aluminum “Carbine” length 1913 rail system is bolted solidly to the front of the receiver. This features rails at 12, 3, 6 and 9 o’clock for attaching accessories. At the bottom rear of the rail is a rather large rectangular keeper locked in place by a U-shaped spring steel retainer.

A look at what is included in the Bug-Out Bag: MCS upper and lower receivers, 5.56x45mm and 9x19mm barrels, bolt assemblies, buffers and mag wells, .22 LR conversion kit and mags.

To install or remove a barrel, first make sure the rifle is unloaded, the magazine removed, and the bolt locked to the rear. Then you unsnap the U-shaped retainer and slide the rectangular keeper forward. Doing so exposes the two locking levers. Rotating these 90 degrees away from the barrel allows the barrel to be removed or one installed. To remove, simply pull it straight out of the receiver. To install, you must line up the gas tube or, in the case of a blow-back operated caliber such as 9x19mm, the barrel index pin. Simply insert the barrel and rotate the locking levers 90 degrees so they run parallel with the barrel. Slide the rectangular keeper over them and lock it in place with the U-shaped retainer. Installing a barrel takes about 15 seconds, and removing one takes about 10 seconds.

The lower receiver assembly also appears to be a standard piece at first glance. Again, it is not. Examining it, you’ll note a standard carbine receiver extension with a Mission First Tactical (MFT) Minimalist Stock. An A2 pistolgrip is also standard. The controls all look traditional and are placed exactly like a standard AR. Even the GI folding trigger guard is there. If you unlatch the front of the trigger guard and rotate it down, then depress the magazine release, the entire magazine well can be slid straight up and off the rear receiver section. Magazine wells are easily interchangeable and take only seconds to swap out if the lower is separated from the upper.

The first time you show this feature to someone, his jaw always hits the floor. It is very simple in concept and nicely executed. As the lower is a two-piece assembly, you will note the rear receiver group is the serialized part. So you can swap mag wells to your heart’s content. Why swap magazine wells? The standard STANAG magazine well is very versatile and allows a wide variety of cartridges to be fired. By swapping it out though, you can replace it with a mag well that accepts Colt pattern submachine gun magazines for firing 9x19mm. Or, you can replace it with a mag well that accepts AK-pattern 7.62x39mm magazines.

Windham Weaponry’s MCS built as a 16-inch 5.56x45 carbine (top). Note the Quad Rail handguard, M4 profile barrel with 1:9 twist rate, flattop upper, and Mission First stock. Here, the MCS has been reconfigured as a 9x19mm Pistol Caliber Carbine (bottom) by changing the mag well, bolt, buffer, and barrel. All this takes about a minute.

Pulling the 16-inch 5.56x45mm barrel from the pack, I noted it to be chrome-lined and an M4 profile. It features an A2 flash suppressor, pinned-on gas block with a rail on top for mounting a front sight, one turn in nine inches rifling twist, and M4 feed ramps. Next, I dropped the 5.56x45mm bolt carrier into the receiver, verified a standard buffer was in place, and assembled the upper onto the lower. The final touch was inserting the included 30-round magazine. The result was a good-looking carbine which just needed sights or an optic.

To convert it to .22 LR, all you have to do is remove the magazine and bolt carrier assembly. Inside the pack, you’ll find a CMMG conversion kit, which slides into the upper receiver, taking the place of the standard bolt-carrier assembly. Next, just insert the included .22 LR 25-round magazine. The conversion kit makes use of the standard 5.56x45mm barrel. While the 1:9 twist is considerably faster than a 1 turn in 16 inches twist standard for .22 LR, it works acceptably well for plinking, recreation, practice and small-game hunting.

To change to 9x19mm, you need to remove the 5.56x45mm barrel and replace it with the included 16-inch 9x19mm barrel. This features a Melonite finish and a 1 turn in 10 inches twist. As the 9x19mm functions via blow-back, no gas block or tube is required or installed. The bolt-carrier assembly must be exchanged for the 9x19mm bolt, and the standard buffer must be swapped out for the heavy 9mm buffer. Lastly, the 9x19mm magazine well needs to be installed and the proper 20-round magazine inserted. This takes about a minute to accomplish. It’s very easy and you only need a 5.56x45mm cartridge or a pen to push in the detent in the trigger guard.


A carbine-length free-floating Quad Rail handguard is standard. The 5.56x45mm barrel features a carbine-length gas system and chrome-lined barrel with A2 flash suppressor. Underneath the Quad Rail is a polymer keeper, which serves to lock the barrel retention levers in place. To remove or install a barrel, first unsnap the U-shaped retainer and slide the rectangular keeper forward. Doing so exposes the two barrel-locking levers. Rotating the barrel-locking levers 90 degrees allows the barrel to be removed by simply pulling it straight out of the receiver. The kit also comes with a CMMG .22 LR conversion kit (bottom right), which replaces the 5.56x45mm bolt-carrier assembly, and one 25-round magazine.

The end result is three calibers you can shoot from one AR. You could use it as a 5.56x45mm for personal protection and, with proper ammunition selection and shot placement, to take whitetail-size game at reasonable distances. Convert it to 9x19mm and it will shoot the same ammunition as your sidearm. It can be used for plinking, practice, competition or personal protection as a 9x19mm. Convert it to .22 LR and you can take small game, practice very economically, or plink. That’s quite a bit of versatility from one rifle. Plus, you can easily swap to additional calibers if you so desire. For example, 300 AAC BLK would require just a barrel. 6.5mm Grendel, 6.8x43mm SPC, .224 Valkyrie, .50 Beowulf or .458 SOCOM would need just a barrel, bolt, and possibly a magazine.

Sounds good, but how does it actually perform? Swapping barrels and magazine wells are indeed very easy. No issues here. Build quality looks good as well. The stock “GI”-type trigger though is heavy and has a bit of creep. Pull weight was approximately seven pounds. I’m not a big fan of stock triggers like this, but they are easily changed by pushing out a couple cross-pins. So upgrading the trigger is not an issue. What about accuracy? To find out just how well the MCS shot, I picked out three loads for each caliber and headed to my range. Bench testing was performed with a 2.5-10x42mm scope, which zeroed without issue. Accuracy was checked at 100 yards for the 5.56x45mm and 9x19mm, and at 25 yards for the .22 LR conversion. Groups were shot from a rest in conjunction with a rear bag.

5.56x45mm test ammunition consisted of Black Hills Ammunition’s 60-grain V-MAX, American Eagle’s 62-grain FMJ, and Federal’s 69-grain Gold Medal Match. Four five-shot groups were fired with each load to get a baseline of how well the MCS shot. Despite a rather heavy and crunchy trigger pull, Black Hills’ 60-grain VMAX load averaged a very respectable 1.2 inches at 2,794 fps. Federal’s 69-grain Gold Medal Match load also shot very well and averaged 1.3 inches at 2,538 fps. American Eagle’s 62-grain FMJ load averaged 2.5 inches at 2,740 fps. No issues were encountered.

The MCS does not come with sights, but the flattop upper receiver makes mounting optics like this 4x32mm ELCAN very easy.

Next, it was time to convert it to 9x19mm. This was easily accomplished, the scope was re-zeroed, and I got back to work. For this portion of testing, I selected Black Hills Ammunition’s 115-grain JHP +P and 147-grain JHP, along with Wolf Performance Ammunition’s 115-grain FMJ. Four five-shot groups were fired from the bench at 100 yards. As I got to work with the blow-back operated 9x19mm, I immediately noticed it exhibits noticeably more felt recoil than the gas-operated 5.56x45mm. The gun moves more as the heavy bolt slaps back and forth. Again, accuracy proved quite acceptable with Black Hills Ammunition’s 115-grain JHP +P averaging 4.3 inches at a healthy 1,548 fps. Wolf Performance Ammunition’s 115-grain FMJ averaged 5.2 inches at 1,338 fps. Black Hills Ammunition’s 147-grain JHP averaged 5.5 inches at 1,110 fps. After finishing the 9x19mm testing, I swapped over to .22 LR. I personally love .22 LR conversion kits and own a few, including a U.S. military M261 RFA and two I purchased from CMMG. I have shot a large number of farm pests using my CMMG kit and love it. Personal experience over years of use has shown me these kits are very reliable if kept fairly clean and well lubricated. Accuracy is usually suitable for small-game hunting and plinking, but certainly not match grade.

One thing to be aware of is all drop-in conversion kits (M261 RFA, Ceiner, CMMG, etc.) utilize a chamber spacer, which sits inside the rifle’s 5.56x45mm chamber. Due to this, there is a substantial amount of freebore before the projectile reaches the rifling. This freebore, combined with a slightly undersized soft lead projectile and the faster twist of a 5.56x45mm barrel is detrimental to accuracy. Another thing to keep in mind is dedicated .22 LR rifles have a 1 turn in 16 inches barrel twist. This is substantially slower than the 1:9-inch twist 5.56x45mm barrel included with the MCS. My personal experience shows it’s best to try as many different loads as possible, as accuracy can vary quite a bit from load to load. This is especially true with an even faster 1:7-inch twist, where I’ve seen some loads shoot awful and others surprisingly well from the same barrel. Find the right load though, and they will put meat in the pot.

The First Response Minimalist collapsible stock (top left) proved comfortable, while reducing weight. While not included in the Bug-Out Bag System, Windham Weaponry does also offer a 7.62x39mm conversion kit (top right), which feeds from AK magazines. A look at the lower receiver with the 9x19mm Colt pattern mag well installed (bottom left). Note the ejector and last-round hold-open. The MCS also allows you to easily change mag wells. Windham Weaponry offers 9x19mm Colt pattern, 7.62x39mm AK pattern and 5.56x45mm STANAG pattern mag wells.

Another thing to keep in mind when using any .22 LR conversion kit in an AR-15 is proper cleaning. Studies conducted by both the U.S. and Canadian militaries showed .22 LR ammunition will foul an M16-type rifle barrel with lead deposits. If left in place, the lead fouling can both raise the pressure when firing 5.56x45mm and negatively affect accuracy. Due to this, you must carefully clean the barrel after firing .22 LR ammunition and before firing 5.56x45mm. Extended use of .22 LR can also plug the gas system, preventing semi-automatic operation with 5.56x45mm. Typically, firing a couple of 5.56x45mm rounds will clean this out. If you are lazy, and think cleaning guns is a drag, you could always keep one barrel dedicated for use with .22 LR. It’s just important to know how to properly utilize and maintain an AR when used in conjunction with a .22 LR conversion kit.

I checked accuracy from the bench at 25 yards. Best accuracy was obtained using Wolf Performance Ammunition’s 40-grain Match Gold, which averaged .5 inch at 1,070 fps. Aguila’s 60-grain SSS averaged .8 inch at 1,000 fps, while Federal’s bulk pack 36-grain averaged 1.4 inches at 1,280 fps. All three loads chugged away without issue, but I noticed I could only fit 23 rounds into the 25-round magazine. Moving from the bench, I cleaned the 5.56x45mm barrel, reinstalled the 5.56x45mm bolt-carrier assembly, and mounted an ELCAN 4x scope with an illuminated BDC reticle. I then spent some time shooting steel plates from 100 to 500 yards with the rifle set up in 5.56x45mm. The rifle functioned without issue, accuracy was acceptable and my only complaint was the heavy trigger. Shooting offhand, kneeling and sitting, I had an enjoyable time shooting plates and silhouettes, and the MCS acquitted itself well.

Swapping back to 9x19mm, I ran the MCS through a variety of drills from 25 to 100 yards. Here, I did run into a couple issues. I borrowed three 32-round Colt-pattern magazines from a friend and two of these failed to feed. One of them worked without issue, as did the included 20-round magazine. So I set the two problem magazines aside and had fun. One of the nice things about a 9x19mm AR is you can safely shoot steel plates at much closer distances than with a 5.56x45mm. The gun jumps a bit more than a 5.56x45mm, but proved a lot of fun to burn ammo through. Lastly, I switched back to .22 LR. I love this little cartridge and really enjoyed my time shooting it. Now that .22 LR ammunition prices have finally come back down to pre-panic prices, I no longer feel guilty for merrily burning through a 500-round brick. The CMMG kit performed well with only a couple hiccups experienced. This is par for the course with an occasional failure to feed to be expected. They are easily cleared and the fun continues.

So far I have listed all the positive features of the MCS, but what are the negatives to this system? Keep in mind that as you swap barrels, you will need to re-zero. The best solution would be to have an optic on a QD mount already zeroed for each barrel. Then you just swap optics as you swap barrels. I prefer LaRue QD mounts, but there are many to choose from. Don’t have the cash for that? Then I would write down the required adjustments so you can keep track of them. You can often get away with using the same scope zeroed for 5.56x45mm with your .22 LR. It may not hit exactly to point of aim, but typically is close enough. Just learn what the actual point of impact is and adjust accordingly.

The MCS proved to be a fairly light and handy carbine when configured in 5.56x45mm. It shot well and proved very reliable.

Another thing to be aware of is that when not actually mounted in the rifle, the unsupported gas tube is sticking out past the end of the barrel. Care should be taken to ensure the gas tube does not get bent. This isn’t rocket science, and I’ve never had an issue with this. When switching from one caliber to another, you need to verify that you have the correct bolt and barrel installed before simply dropping the hammer. This is an absolute MUST. Safety first. It’s very easy to rush, especially if friends are around and make a mistake, so stop and make sure you have the proper barrel, bolt and magazine. I will also say I am not a fan of “Old School” 1913 Quad Rail handguards. It’s not 2005, anymore. They are bulky and uncomfortable without rail covers. With rail covers, they get even bulkier. Luckily, Windham Weapons does offer an alternative. This is nicely streamlined, light weight, and allows you to use either MLOK or KeyMod accessories. Also, due to the Quad Rail being so short and the use of a 1913 rail on top of the gas block, which gets very hot with use, it’s easy to get your hand a bit forward and burn a finger. Do it once, and you’ll keep your fingers away from the gas block.

The MCS proved to be a fun shooter when configured in 9x19mm. Recoil is a bit heavier than in 5.56x45mm and accuracy proved quite acceptable.

What are the positive features of this system? On the plus side, you can easily swap barrels and calibers using one basic rifle. You don’t need complete upper receiver assemblies, like with a standard AR. This saves money and space. Plus it utilizes standard AR barrels. So you can buy a 6.5mm Grendel or .450 Bushmaster barrel, bolt, gas block, and gas tube and have a new gun. Not only can you swap barrels, but you can swap operating systems as well. That’s right, you can install a piston assembly if you so choose, so you can easily set the rifle up exactly the way you want it. Plus, the carbine can be disassembled into a relatively small package. By removing the barrel from the upper, and then popping the upper off the lower, you end up with three relatively short pieces. These will store neatly in a space you would not expect a 16-inch carbine to fit into. There is also the ability to utilize a wide array of existing magazines in different calibers. Windham Weaponry’s MCS very neatly adds some very interesting features to an AR. I greatly appreciate the fact that it uses off-the-shelf barrels and parts, rather than some hard-to-find specialty pieces. While a surprising amount of calibers will fit into the standard AR mag well, the MCS handily extends your options. Do you need an AR with the ability to swap barrels and mag wells? That’s up to you to decide. But, if such a beast appeals to you, this is one to consider. Price for the complete system seen here, with backpack and survival kit, is $2,495. Too much? Windham Weaponry also offers a two-caliber kit, 5.56x45mm and 300 AAC BLK, for $1,738. Plus, the company has more on the way, so keep an eye on its website.


Windham Weaponry MCS Bug-Out Bag

  • Action: Rotating bolt via direct gas/blow-back
  • Caliber: 5.56.45mm, 9x19mm, .22 LR
  • Barrel: 16 in. Gov. profile
  • Rifling: 5.56mm: 1:9-in. twist, 9mm 1:10-in. twist
  • Overall Length: 35.7 in. 
  • Trigger: Standard single stage
  • Feed: Detachable box mags
  • Sights: None, Picatinny rail
  • Weight: 6.9 lbs.
  • Finish: Parkerized
  • MSRP: Discontinued by Manufacturer 

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