One Horse Complete AR-15 Upper Receiver - 300 Blackout - 10.5"

The One Horse Complete AR-15 Upper Receiver in 300 Blackout pairs a 10.5" medium profile 4150 steel barrel with a 10" M-LOK free-float handguard, built to mil-spec standards in the USA.

Features:

• 10.5" medium profile 4150 steel barrel, nitride treated
• Pistol-length gas system
• 10" M-LOK free-float handguard, steel barrel nut
• Nitride bolt carrier group
• Standard charging handle (included)
• 5/8x24 threaded muzzle
• Made in the USA

4150 steel carries higher carbon content than the 4140 used in many entry-level AR-15 barrels, giving this barrel improved wear resistance at the bore and chamber under sustained firing, and the nitride treatment adds a hard, corrosion-resistant surface comparable to chrome lining without adding measurable thickness. The free-float M-LOK handguard keeps the barrel isolated from contact pressure that degrades harmonics, and the steel barrel nut gives a more rigid handguard-to-upper connection than an aluminum nut under repeated thermal cycling.

Because this 10.5" barrel measures under 16", this complete upper is intended only for an AR pistol or a legally registered short-barreled rifle — attaching it to a standard rifle lower without the correct configuration violates federal law.

One Horse builds its complete uppers in the USA around 4150 steel barrels and nitride bolt carrier groups, aiming for mil-spec reliability at an accessible price point.