Barnes 300 Blackout
Barnes 300 Blackout with 11.5-inch barrel has Magpul stock, pistol grip, and folding sights. Ultralight foregrip and rail system are proprietary BPM. Gas tube is adjustable for subsonic ammo, but works best with suppressor. Montana match barrel is capped with BPM A2-style muzzle device with breaching tip.

Most S.W.A.T. readers have heard the good news about the .300 Blackout (aka .300 Whisper and 7.62x35mm) caliber. I have not written dedicated articles about the cartridge, but became familiar with its flexible performance capabilities by evaluating various AR launching platforms for it.

Once again, I have the pleasure of revisiting the .300 BO with a Barnes Precision Machine (BPM) .300 Blackout (BO) Carbine with 11- and 16-inch upper receivers. In addition to this weapons platform, I was able to acquire a number of unusual bullet weights from manufacturers that have little or no notoriety.


As I have quipped before, maybe the Russians were right after all, because the .300 BO has similar, but notably better, long-range performance than its 7.62x39mm Kremlin cousin, primarily due to its better ballistic coefficient.

And while not as flat shooting, it is superior to the 5.56x45mm in most respects. With the development of bullet weights ranging from 110 to 250 grains, the caliber gives us excellent supersonic and subsonic performance in long and short weapons configurations. Its lethality is further augmented by the development of hollow and soft point bullet designs.

The Blackout’s most notable advantage is its ability to use necked-up .223/5.56x45mm brass, AR magazines and AR bolts. All that is needed is the correct barrel assembly.

SBR field stripped with Nickel Boron bolt carrier with components visible. Charging handle is from M&P Parts. Adjustable stock and pistol grip are Magpul. BPM muzzle device with breaching tip reduces muzzle blast and felt recoil.


Among the relatively small cadre of custom gun makers that turn out superb firearms and have been primarily responsible for the continued advancement of the AR rifle breed, Barnes Precision Machine has added their entry to the growing number of .300 BO platforms.

Whether the caliber is or is not adopted by the military/police (MILPOL) communities, artisans like Andrew S. Barnes are betting it will become popular with citizen shooters.

BPM has been in the business of building AR parts since 1996, and match capable and MILPOL service weapons since the late 1990s. Over a dozen OEM parts manufacturers buy from BPM, so chances are that your other manufacturer’s AR has BPM components in it. In fact, the AR industry in general, including the big boys, relies on BPM for many of the featured items on their creations.

However, unlike other gun stables that produce every imaginable version of “America’s Rifle”, BPM has focused on only four AR variants. The .300 BO most closely resembles BPM’s CQB-Patrolman’s Carbine. Unlike a number of AR shops that are essentially aggregators and assemble their black rifles with parts made by myriad component manufacturers, BPM produces 95% of the guts used in their guns.

The carbine’s foundation is BPM’s 7075 forged milspec CNC-machined hard-anodized lower receiver with accurizing screw and rear detent set screw. The accurizing screw acts like an “Accuwedge” that many shooters slip into their receivers to establish a very tight fit between the upper and lower for a potential increase in accuracy.

The accurizing attribute is married to heattreated, hand-lapped and polished stainless steel Montana Rifleman’s barrel blanks protected with black magnesium phosphate. These BPM CNCmachined barrels are available in lengths from 11.5 to 20 inches with a 1:8 twist. Currently BPM is evaluating fluted barrels to reduce weight.

Proprietarily, BPM manufactures a fully weighted “full-auto style” milspec bolt carrier group that is finished with a Nickel Boron (NiB) process by WMD Guns. The NiB bolt carrier reduces friction, is easier to clean, and has slicker cycling. It requires less lubrication, is corrosion resistant for maritime operations, and has an extremely hard surface that reduces wear and increases components’ lives.

The bolt carrier construct is milspec with carpenter 158 or 8620 alloy steel, NiB processed cam pin, hardchromed firing pin, and milspec staked gas key.

Other features of the carbine include Magpul MOE stock, pistol grip with storage compartment, and pop-up back-up sights with front sight adjustment tool. BPM includes its A2 flash hider with “breaching tip,” Commercial Grade AR-15 semiautomatic fire-control group, and carbine length adjustable gas system. Suggested retail is $1,608.60.

BPM has also developed the Ultralite Extreme rail system for its Ultralight Handguard that mates with Magpul Rail Sections and can be mission-specific configured as well as for run-and-gun competitions.

Full-length Picatinny rails crown its dorsal surface and use a BPM proprietary barrel nut design. The barrel nut locks the free-floating barrel into the receiver, which results in increased handguard rigidity and better barrel harmonics. Its militarystyle trigger is two-stage with little take up, a short reset, and breaks crisply at a consistent five pounds.

Five quick-detach steel sling swivel inserts/points and a removable bipod insert with appropriate hardware facilitate its utility and assist the weapon in fulfilling a special purpose rifle role.

Overall length with stock extended is 36¼ inches and 33 inches collapsed. Overall dry weight with sights is 7.04 pounds. With 30 125-grain stored kills on board, its go-to-war weight increases to eight pounds. The above specs are for the 16-inch barrel model.

William Hiett demos his high ready and gun mount with SBR.

The complete package includes a Patriot hard case, one PMAG and manual. No particular brand of lubrication is recommended, although the BPM representative used Frog Lube during our shooting evaluations. BPM provides fixed scope mounts if desired.


With the aid of a Leupold Mark 4 MR/T 1.5-5X20mm optic, the Barnes representative shot the 16-inch carbine from a prone position, addressing the subsonic rounds first. We immediately experienced problems with cycling and in some cases bullet stability. Both 200-grain Coopers would not cycle and keyholed, albeit accurately, into the target at 50 yards. Two hand-cycled CorBon 240s also yawed into the paper but produced a .720-inch group. Hornady 208-grain cycled inconsistently yet delivered the best cluster of the day at 0.60 inch.

During chronographing, one 194-grain Lehigh Defense round experienced a bolt-over-bullet stoppage. Both the carbine and SBR experienced similar cycling problems even with a fully opened gas port. Barnes advised that its carbines require a suppressor to produce adequate backpressure to function with subsonic ammunition.

Conversely, all supersonic cartridges cycled flawlessly. High individual velocity honors went to Ventura 110-grain Controlled Chaos at 2,447 feet-persecond (fps) and 1,498 foot pounds of kinetic energy, significantly less than what is delivered by 7.62x39mm at the muzzle. Both guns were as controllable as a 5.56x45mm carbine, although with a more push-like felt recoil and a bit more muzzle rise, particularly with the heavier bullets.

Without suppressor attached, one bolt-over-bullet stoppage was experienced with subsonic ammo. Even with gas tube adjusted,
majority of subsonic rounds had to be hand cycled.

Second Attempt

Things were different the next time former Marine William Hiett and I met to reshoot the subsonic ammunition that the .300 BO had choked on. Our problems with bullet keyholing and failures to function with the heavy weights were dramatically solved by the addition of the compact, quick-attach AAC SD NC suppressor.

Regardless of weight and configuration, all rounds punched clean holes through the target and functioned flawlessly. Ejection was robust and to the right rear. In concert with the AAC can, the BPM gas tube was fully opened.

As an aside, a federal agency that fields a dedicated security team for its principal and has a Tier One counterterrorist unit is also employing .300 BO, AR-15 style weaponry. The agency’s armorers have been able to tune issued weapons so they will digest the full spectrum of supersonic and subsonic .300 BO bullet weights without any adjustments.

All subsonic rounds, 174 to 245 grains, were fired from prone at 50 yards. All supersonic rounds were fired from prone at 100 yards. Three-shot groups were fired for accuracy and five-shot strings were fired through an Oehler 35 P chronograph to obtain average velocities.

Top Shot All Stars William Bethards double taps through 30-round PMAG with BPM SBR. CQB-length carbine handled like full-sized .300 BO, albeit with more, but tolerable, muzzle blast.


Our crew ran the 11.5-inch carbine through the sky screens with four selected loads. The 245-grain subsonic slugs averaged 1,013 fps, Hornady 110-grain averaged 2,297 fps, Jamison 150-grain cruised through at 1,878 fps, and Steadfast 125-grain registered a 2,025 fps average for the five rounds fired for each load.

When compared to the 16-inch barrel, expected velocity loss for the supersonic rounds was not that significant, but more than 100 fps was lost with the heavyweight subsonic load in the shorter tube. In either barrel length, heavy subsonic bullets act more like hot handgun rounds in terms of kinetic energy.



The quest for a new military rifle cartridge may never end. That quest may also be accompanied by a new weapons platform with capabilities beyond just launching a single high-velocity projectile. How soon that occurs will be economy dependent.

In the meantime, companies like BPM will make the highest quality iterations of the AR weapons system. In addition to meeting and exceeding current standards of excellence (with the competition continuing to raise the bar), BPM offers its products at extremely reasonable prices.

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