I always liked the idea of folding stocks, but being a diehard AR guy, that wasn’t generally an option. Unless you went with something like a LAW folding buffer system. Thanks to bufferless uppers from Foxtrot Mike and Brownells, though, I can finally join the folding stock crowd, too. B5 Systems dropped its Modular Platform Stock earlier this year, and I decided to snag one and see what they were all about.
The Modular Platform Stock from B5 Systems
The B5 Systems Modular Platform Stock (MPS) is a rugged and highly adaptable stock. It features an integral left-side folding steel hinge for compact storage and transport. The MPS offers a 2 1/4 inch collapsible length of pull adjustment for a customizable fit.
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The adjustable spring-assist cheek piece adds 1/2 inch of height for proper sight alignment. It’s easily manipulated by pulling back and either pushing up or down. The MPS is made from durable composite materials with color-matched steel hardware.
The stock comes with a cushioned, non-slip buttpad for enhanced shoulder contact. It supports ambidextrous use with fixed sling mounts and steel anti-rotational quick disconnect (QD) sling mounts. The stock attaches securely via a 1913 Picatinny mount. It’s available in Black, Wolf Grey, Flat Dark Earth, Coyote Brown, and OD Green.
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Weight is just 16.8 ounces, and it measures 8.06 inches long, 1.76 inches wide, and 4.67 inches high. Like all B5 Systems products, the Modular Platform Stock is made in the USA.
Not Just For AR’s
While I’m always a little AR-centric, the B5 Modular stock will fit on anything with a Picatinny rear mount. This opens it up to any number of pistol-caliber carbines. It will also work with .22 Rimfire AR’s since they don’t need a buffer. It even works on shotguns.
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I initially used the MPS on my KE Arms/Foxtrot Mike SBR build. It worked extremely well on that rifle. The SBR folded to a very compact 23 3/4 inches with the stock folded to the side. The stock sat high enough that you could still access the grip, trigger, and fire controls when folded as well. That allows you to fire the rifle with the stock folded if need be.
Extended, the lock-up is solid and feels like you’re firing with a fixed stock. It’s far more stable than most of the AK side and under folders I’ve used in the past. The rubber butt pad seats firmly in your shoulder pocket. The stock easily adjusts for length of pull as well. You can quickly adapt it for arm length, body armor, or heavy clothing use.
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Mossberg 590 Fit
B5’s MPS was a good fit on the KE/FM build, but I had other long-term plans for that one. I decided to see what else I could use it for from my collection.
When I picked up the KE Arms lower, I also got a Picatinny adapter for the Mossberg 500/590 series shotgun. While I’ve been tempted to Form 1 my Mossberg Shockwave, I decided to run it on my old 590A1 for now.
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My 590 has a 20-inch barrel, so with a fixed stock, it’s a fair-sized gun. Adding a folder makes it a little more compact for storage in the Jeep. I installed the KE Arms Pic adapter and added the B5 MPS, along with a B5 P-Grip 22, to the shotgun.
The KE Arms adapter installed easily with the included bolt and lined up perfectly with the Mossberg Receiver. The B5 grip is attached with a standard AR grip screw, and the Modular Stock is bolted to the rear Pic rail. While the stock is inline, I was still able to comfortably use the factory ghost ring sights on my 590A1.
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The other thing I tried the MPS on was an AR lower I have fitted with a Picatinny rear rail. I use the lower with a brace and my Solo 300 pistol upper. It also works with a variety of rifle uppers and my CMMG .22 conversion kit.
You don’t need a buffer system with the CMMG conversion, so you can use any .223/5.56 upper. You just need to swap out the bolt and magazines to shoot .22LR, then.
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Since the MPS installs on the Pic rail, it’s easy to swap back and forth between it and a brace. That lets me readily swap between rifle and pistol configuration with that lower. It started as a stripped lower, and is registered as such, so it’s kosher to swap back and forth to proper legal configurations.
Wrap Up
With B5 System’s Modular Platform Stock, you get all of the advantages of a side-folding stock, with the shooting properties of a fixed stock. It has an MSRP of $200.00, which is competitive with other stock solutions on the market. If you have a rifle, shotgun, or PCC with a Picatinny rail and want something more substantial than a skeletonized stock, the B5 Systems Modular Platform Stock is a very viable option.
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