The Rock River Arms .450 Bushmaster Complete Upper (brand part number 450B0461) pairs a forged A4 receiver with a 16-inch, cryogenically treated stainless steel barrel cut with a 1:24 twist, sized to stabilize the heavy, straight-walled .450 Bushmaster projectile. At 16 inches, the barrel clears the federal rifle-length minimum, so no NFA paperwork is required. RRA threads the muzzle 5/8-32 for its own Operator Brake, which ships installed, and runs a low-profile gas block on a mid-length gas system for softer cycling. A 13-inch extended, lightweight free-float M-LOK handguard covers the barrel, and the upper ships complete with a bolt carrier group, charging handle assembly, and one 5-round magazine.

Key Specifications

• Chambered in .450 Bushmaster.
• Barrel length of 16 inches, clearing the federal rifle minimum.
• Barrel is stainless steel, cryogenically treated.
• Twist rate of 1:24.
• Receiver is forged A4.
• Includes the RRA Operator Brake, threaded 5/8-32.
• Runs a low-profile, mid-length gas system.
• Handguard is a 13-inch extended, lightweight free-float M-LOK rail.
• Includes a bolt carrier group and charging handle assembly.
• Includes one 5-round magazine.

Frequently Asked Questions

Does this include a lower receiver? No, this is a complete upper; it requires a compatible AR-pattern lower to build a complete rifle.

Is a 16-inch barrel legal without NFA paperwork? Yes, 16 inches clears the federal rifle minimum.

What comes included with this upper? The BCG, charging handle assembly, and one 5-round magazine.

Buy the Rock River Arms .450 Bushmaster Complete Upper

Add serious close-range stopping power to your AR-pattern lower. Order this .450 Bushmaster upper from Rock River Arms through our AR15 uppers lineup, and our Lubbock, Texas team will get your order ready to ship as soon as it’s available.