The Radical Firearms 10.5in .300 Blackout Complete Upper (brand part no. RF00358) is built around a 10.5-inch HBAR-profile barrel and is a complete MIL-STD upper ready to drop onto any MIL-STD lower receiver. It’s finished with Radical’s 10-inch RPR free-float M-LOK rail system, keeping hands cool and adding accuracy-friendly rigidity, whether the shooter finishing the build is a novice looking to complete their first rifle or an experienced builder adding another platform to the safe. Because this upper does not include a lower receiver, it is not by itself a regulated firearm; how it’s ultimately configured once installed on a lower determines its legal classification, covered further below.

Key Specifications

• Chambered in .300 AAC Blackout.
• 10.5-inch HBAR-profile barrel.
• Complete MIL-STD upper, ready for any MIL-STD lower.
• 10-inch RPR free-float M-LOK rail system.
• Finished in black.

Frequently Asked Questions

Does this upper include a lower receiver? No, it’s a complete upper only and drops onto any MIL-STD AR-15 lower.

Is a 10.5-inch-barrel upper without a lower a regulated firearm? No. A bare upper is not itself the regulated part. Putting it on a shouldered rifle lower makes a short-barreled rifle; since October 9, 2026, ATF no longer requires Form 1 approval or registration for that, but state law still applies, and taking an SBR across state lines needs an approved ATF Form 5320.20.

What handguard does this upper use? Radical’s 10-inch RPR free-float M-LOK rail system.

Buy the Radical Firearms 10.5in .300 Blackout Complete Upper

Finish your 300 Blackout build and hit the range. Order the Radical Firearms upper from our AR15 uppers selection at our Lubbock, Texas gun shop as soon as it’s ready to ship.