The Radical Firearms 300 Blackout Upper (brand part no. RF00375) is a complete, mil-spec AR-15 upper chambered in .300 AAC Blackout, built around a 16-inch barrel with a 1-in-8 twist rate and topped with an M-LOK handguard. Because the upper is built to mil-spec dimensions, it drops onto any standard mil-spec AR-15 lower receiver without additional fitting. .300 Blackout gives shooters the option to run both supersonic and subsonic loads through the same barrel, making it a versatile chambering for hunting, home defense, or suppressed shooting. Radical Firearms builds this upper for shooters finishing out a build or upgrading an existing rifle, whether they are new to the platform or experienced at the range.

Key Specifications

• Chambered in .300 AAC Blackout for supersonic and subsonic versatility.
• 16-inch barrel clears the federal rifle minimum for use under a fixed or adjustable stock.
• 1-in-8 twist rate stabilizes the range of .300 Blackout bullet weights.
• M-LOK handguard adds mounting space for lights, grips, and optics.
• Built to mil-spec dimensions for drop-in fit on any standard AR-15 lower.
• Sold as a complete upper, ready to install.

Frequently Asked Questions

Will this upper fit any AR-15 lower? Yes, it is built to mil-spec dimensions and drops onto any standard mil-spec lower.

Can this barrel run subsonic ammunition? Yes, .300 Blackout is designed to cycle reliably with both supersonic and subsonic loads.

What twist rate does it use? A 1-in-8 twist, suited to the full range of .300 Blackout bullet weights.

Buy the Radical Firearms .300 Blackout Upper

Finish your build with a versatile, mil-spec .300 Blackout upper ready for the range. Order this Radical Firearms upper from our AR15 uppers selection, and our Lubbock, Texas team will get it ready to ship as soon as it’s available.