One Horse OH-15 AR-15 300 BLK 10.5" 30rd Pistol

300 BLK was designed around exactly this barrel length, so the OH-15 at 10.5" is the configuration the cartridge was built for. Unlike 5.56, which gives up meaningful velocity every inch you cut, 300 BLK burns its powder in a short tube and loses almost nothing. Supersonic loads hit hard up close and subsonic loads run quiet behind a can, and both cycle off the carbine gas system here. The muzzle is threaded 5/8x24, the standard for 30 caliber, with an A2 device installed and a 1:8 twist behind it.

Everything else is straight AR-15. Mil spec buffer tube, standard charging handle, A2 grip and a 9.25" M-LOK handguard that leaves room for a light and a hand stop without carrying rail nobody uses. A KAK brace sits on the buffer tube and one 30 round magazine is included. Because 300 BLK shares the bolt and the magazines with 5.56, an owner who already runs an AR can swap uppers or feed this one from the mags already in the range bag. Keep the two cartridges separated and labeled, though: 300 BLK will chamber in a 5.56 barrel and the results are ugly.