.300 AAC Blackout

The .300 AAC Blackout — also written as .300 BLK or 7.62x35mm — is a cartridge engineered from the ground up with one question in mind: what does suppressed performance actually look like when you design for it intentionally? The answer is a round that runs in a standard AR-15 with nothing more than a barrel swap, cycles reliably with a suppressor in both subsonic and supersonic configurations, and delivers genuine terminal performance at practical ranges.

It fires a .308-inch bullet — same as the .30-06 and .308 Winchester — but in a package sized for the AR-15 platform. Subsonic loads push 220-grain bullets at 1,050 fps or so. Supersonic loads push 110 to 125-grain bullets past 2,200 fps. Two completely different personalities in the same gun. That’s the whole idea.

The .300 BLK was developed by Advanced Armament Corporation and Remington Defense around 2010. The U.S. military — specifically special operations — had long wanted a .30-caliber option for the M4 platform that could run suppressed without the awkwardness of dedicated subsonic weapons or the magazine and bolt changes required by earlier solutions like the .300 Whisper.

AAC’s Kevin Brittingham and his team came up with something elegant: take .223 Remington brass, cut it down, open the neck to .308, and seat a heavy bullet. The result feeds from standard STANAG magazines at standard capacity, uses the same bolt as a 5.56 AR, and only requires a barrel change to convert. SAAMI standardized it in 2011. Suppressors went mainstream. The .300 BLK had a moment and never really stopped having it.

Here’s where the split personality really shows up. Supersonic .300 BLK with a 110 to 125-grain bullet exits at 2,100 to 2,350 fps and hits with 1,200 to 1,500 ft-lbs at the muzzle. That’s legitimate deer and hog hunting performance at woods ranges, and it’s noticeably harder-hitting than 5.56 in terms of projectile diameter and energy transfer at close range.

Subsonic loads are the magic trick. A 220-grain bullet at 1,050 fps — with a suppressor — produces a sound signature that’s genuinely movie-quiet. The suppressor doesn’t have to fight supersonic crack. All you hear is the action cycling and a muffled thump. For home defense, suppressed hunting, or any application where hearing protection isn’t practical, it’s a legitimate game-changer. The tradeoff is range — subsonic loads drop like a rock past 150 yards and deliver modest terminal energy, so use them appropriately.

Home defense with a suppressor is a huge use case — the reduced sound signature means you can run your rifle in a defensive situation without permanent hearing damage. Hog hunting, especially at night with a suppressor, is another killer application; hogs are social animals and a quiet gun means you can keep shooting. Deer hunting at woods ranges is legitimate with supersonic loads and the right bullet construction.

The military and law enforcement application that spawned it — close-quarters work with subsonic ammo — is alive and well in civilian form. Competition shooters run it. Backyard plinkers run it. It’s become a platform in its own right. If you already own an AR-15, getting into .300 BLK is as simple as buying a barrel. That low barrier to entry has driven enormous adoption.

Every major AR-15 manufacturer makes a .300 BLK variant: CMMG, Daniel Defense, BCM, Aero Precision, Ruger, Sig Sauer, and a hundred others. You can buy a complete rifle, a complete upper, or just a barrel — your call. The modularity of the AR platform means you can share lowers, triggers, stocks, and grips between your 5.56 and .300 BLK uppers. It’s one of the most cost-effective ways to add a second caliber to your safe.

Bolt-action options exist too, for the precision crowd who want to run subsonic quietly without semi-auto action noise. Remington, Ruger, and Savage have all offered bolt guns in .300 BLK. Pistol-length AR builds are extremely popular in this caliber — the cartridge was designed to perform from short barrels, so a 9-inch pistol build loses very little velocity compared to a 16-inch rifle. That makes it a genuinely effective compact package.

Availability has improved dramatically since 2020’s shortages rattled every caliber. Major manufacturers — Federal, Hornady, Remington, SIG, Barnes, Gorilla, and Sellier & Bellot — all produce .300 BLK in both supersonic and subsonic configurations. You’ll find it at most gun stores and online retailers without trouble in normal times.

Cost is higher than 5.56 — plan on $1.00 to $1.50 per round for quality supersonic hunting and defense ammo, and $1.25 to $2.00 for premium subsonic loads. It’s not a bargain blasting caliber, but it was never designed to be. Reloading makes a substantial difference in cost and lets you tune subsonic loads precisely — the .300 BLK reloading community is large and well-documented.

If you’re building a suppressor host or you already have a can and want to feed it right, Arms East is the place to have that conversation. We stock supersonic and subsonic .300 BLK ammunition, uppers, complete rifles, and the parts to build your own. The guys here actually shoot suppressed — this isn’t theoretical for us.

Come in and tell us what you’re trying to do. Home defense build? Hog hunting rig? General-purpose suppressor host? We’ll point you in the right direction without overselling you on stuff you don’t need. That’s what a good gun store does. Find us in store or browse what we have online at Arms East.