The One Horse 10.5in .300 Blackout Complete AR15 Upper (part no. OH-CU05) is a fully assembled upper chambered in .300 Blackout, sold without a lower receiver. One Horse builds this with a 1:7 twist barrel fast enough for both supersonic and subsonic .300 Blackout loads, ready to drop onto a compatible mil-spec lower.

Key Specifications

• Sold as a complete upper, with barrel, bolt carrier group, and charging handle already installed.
• Chambered in .300 Blackout, a cartridge purpose-built for short-barreled AR15s.
• Cut to 10.5 inches, a common length for short-barreled pistol and registered SBR builds.
• Rifled at a 1:7 twist rate, fast enough to stabilize both supersonic and subsonic .300 Blackout loads.
• Ships at approximately 3.8 lb, in line with a complete short-barreled upper assembly.

Frequently Asked Questions

Does this upper include a lower receiver? No, this is the upper assembly only; you supply a compatible lower.

Is this upper ready to fire out of the box? It comes with barrel, BCG, and charging handle installed, so it just needs a compatible lower to complete the rifle or pistol.

Is a barrel this short legal to buy? Yes. A bare barrel, or a complete upper with no lower attached, is not itself a regulated firearm under the NFA. It only becomes a regulated Short-Barreled Rifle if it’s built onto a rifle-configured lower with a shoulder stock at an overall barrel length under 16 inches without prior ATF approval; pairing it with a pistol lower/brace setup or an already-registered SBR avoids that issue.

Buy the One Horse 10.5in .300 Blackout Complete Upper

Order this complete .300 Blackout upper from One Horse. Ships fast from a Lubbock, TX gun shop. See our full AR15 uppers selection for more build options.