Although the CPS attaches to a standard M4 receiver extension, it includes all the granular adjustability of fixed PRS stocks. (Jim Grant photo)
December 23, 2024
By Jim Grant
One of the AR-15's most appealing aspects as a weapon system is its modularity. The same lower can be used to build a 300 AAC Blackout short-barreled rifle (SBR) suppressor host (with tax stamp), a 9mm pistol caliber carbine, or a long-range precision rifle. This same modularity also allows a shooter to fully customize a gun to fit them perfectly for their desired application. This is crucial to maximize a gun's ergonomics, and no aspect of a gun better accomplishes this than the stock.
The most common AR-15 stock is the collapsible M4 stock. Lightweight, adjustable and inexpensive, it’s an obvious choice for shooters who want a gun that fits them perfectly but don’t want to spend a small fortune on furniture. While dozens of AR-15 furniture manufacturers produce hundreds of different stock variants, my favorite company is B5 Weapon Systems . B5 has been around since 2008 when it began developing and producing its own Special Operations Peculiar MODification (SOPMOD) stock.
B5 systems cut their teeth building and later improving upon the SOPMOD M4 stock like this one shown on a SIG Sauer 516. (Jim Grant photo) B5 Systems Military Origins The original SOPMOD stocks seem to be based on early Colt ACR stocks, which were designed to improve upon the original M4 collapsible stock. Dave Armstrong, the inventor of this stock, patented the design in 2002 to meet the requirements set forth by the Naval Surface Warfare Center Crane Division (NSWC) a few years before the beginning of the War on Terror.
Armstrong’s design was picked up by the Naval Surface Warfare Center, Crane Division and further refined before production was outsourced to Lewis Machine and Tooling (LMT). LMT production was good but costly. Seeing an opening for themselves, B5 Systems picked up a government contract to produce SOPMOD stocks in 2010 and production began the following year. Field reports indicated that soldiers were happy with the new stocks, and despite being less expensive than LMT stocks, the B5 SOPMODs were every bit as durable.
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My experience with the B5 Enhanced SOPMOD Stock didn’t come for a few more years until I ran one on an instructor’s select-fire SIG Sauer 516 at the SIG Sauer Academy in New Hampshire. The stock’s combination of increased cheekspace, rubberized butt plate, and enlarged controls instantly won me over. I liked it so much that I ended up buying half a dozen of the stocks in various colors for both AR-15 builds and any firearm that can take an M4 stock. The only exception to this was on designated marksman-style guns.
(Jim Grant photo) These guns normally feature a longer barrel, a heavier caliber than the 5.56 NATO/.223 Rem., and, most importantly for our B5 stock, they use a larger optic — one that normally doesn’t sit at the same height as prismatic sights commonly found on military-issue M4 carbines. My solution was to adjust my cheekweld and/or duct tape a section of pool noodle to the top to give me a higher comb, but this was far from ideal. Thankfully, the engineers at B5 Systems developed a much better solution to my PRS/DMR build woes — the Collapsible Precision Stock or CPS .
B5 Systems Collapsible Precision Stock The first thing that turned me on to the CPS was that it didn’t use the full-length receiver extension normally employed by PRS stocks, like the excellent Magpul PRS stock. This gives the host rifle the best of both worlds. It’s more compact and easily adjustable with all the fine-tuning of a traditional PRS stock.
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In fact, the B5 CPS stock features a fully adjustable length-of-pull buttpad that extends when the vertical dial is rotated counter-clockwise. Above this, a horizontal dial raises or lowers the comb height, allowing shooters to get the perfect sight picture with their enlarged optic. And unlike most of B5’s competitors, the CPS isn’t terribly heavy, weighing around 21 ounces. This is heavy enough that the gun won’t feel nose-heavy with the B5 installed but not so heavy that the stock would be inappropriate for use on a lightweight carbine.
Notice how the comb height and length of pull are fully adjustable on the CPS. (Jim Grant photo) One of the most underrated aspects of the B5 Collapsible Precision Stock is the adjustment lock button on the bottom of the stock. On traditional, adjustable M4/AR-15 stocks, the adjustment latch must be pushed beyond its regular range of motion to fully detach from the buffer tube/receiver extension. This is a pain to do without some sort of tool since the locking tab is under a great deal of spring tension. On the B5 CPS, the locking tab that secures the stock is easily locked in place by pushing a small tab forward. This means a shooter can easily remove or install the stock with one hand.
As I mentioned earlier, the stock of a rifle is the most influential aspect of its design in terms of ergonomics. An ill-fitting or flimsy stock can make even the most high-dollar firearm feel like cheap junk. Thankfully, the B5 Collapsible Precision Stock doesn’t disappoint. Built from aluminum-reinforced high-density polymer, the B5 CPS feels like a serious piece of equipment. While I haven’t tried to destroy it, I did some basic run-and-gun training with the stock, and it took plenty of abuse that would obliterate cheap polymer stocks.
Regarding fit, the B5 CPS has little play when installed on a Mil-Spec buffer tube. I installed it on several different firearms to further test whether the stock is within spec or not. These host guns included three PSA AR-15 carbines, a LaRue Tactical SBR and a SIG Sauer 516 carbine. On all the guns tested, the B5 CPS was easy to install and rock-solid when mounted on the gun.
As for the controls themselves, the adjustment tab completely surpassed my testing expectations. It was easy to rapidly change the stock length, even when the shooter was in the prone position. As for the comb and length of pull dials, they, too, were easy to adjust. Both the comb and LOP dials are simply oversized screws that extend when turned counter-clockwise. Ideally, I would prefer these to be mechanical dials that “click” into place as the shooter rotates the dial. However, given the tight controls, no amount of normal or even reasonably hard use will shift their position.
The B5 Systems CPS stock fits your long-range AR like a glove. (Jim Grant photo) Versatility One overlooked aspect of the B5 CPS is that it functions well on a wide variety of firearms—even though it is not normally associated with PRS-style stocks. For instance, I found that it was very comfortable when installed on both my Galil ACE Gen II 5.56mm carbine and my SBR’d Palmetto State Armory AK-V 9mm.
Yes, it is heavier than the types of stocks traditionally used on both of these guns, but the added weight is actually beneficial to the Galil in its stock configuration and the AK-V when equipped with a suppressor. Both of these firearms tend to be nose-heavy, and the added weight of the Collapsible Precision Stock functions as a counterbalance weight that shifts the center of balance closer to the shooter. This makes both firearms feel much more comfortable to shoulder for long durations.
While it ultimately depends on a shooter’s needs and the host gun, I give the CPS a firm thumbs up. Its balance of durability, plethora of functions and reasonable price point make it a must for shooters looking to build an AR-15 precision rifle without breaking the bank. Compared to alternative options from other major manufacturers, the B5 CPS doesn’t skimp on features or quality while delivering a stock that not only matches but surpasses the competition. But shooters shouldn’t really be surprised by this, given the high-quality nature of B5’s other stocks, handguards and pistol grips. Ultimately, if you’re looking for a quality PRS stock that fits any mil-spec AR buffer tube, the B5 Systems Collapsible Precision Stock is a must.
