Rock River Arms RRA 450B0461 .450 Bushmaster 16-inch Upper

This Rock River Arms RRA 450B0461 is a complete .450 Bushmaster AR-style upper built on a forged A4 receiver with a 16-inch stainless steel barrel. The assembly features a mid-length gas system, cryogenically treated heavy barrel, and a 13-inch free-float M-LOK handguard. It ships with a bolt carrier group, charging handle assembly, and one 5‑round magazine.

Key Specifications

• The caliber is .450 Bushmaster.
• The barrel measures 16 inches and is stainless steel.
• The barrel is described as heavy.
• The twist rate is 1:24.
• The muzzle device is the RRA Operator Brake (5/8-32).
• The gas system uses a mid-length gas system with a low-profile gas block.
• The handguard is a 13 inch extended lightweight free-float rail compatible with M-LOK accessories.
• The barrel has been cryogenically treated.
• The upper receiver is a forged A4 receiver.
• Includes a bolt carrier group, charging handle assembly, and one 5-round magazine.

This complete upper provides a robust platform for applications where a large-bore AR configuration is desired. Its stainless heavy barrel and extended free-float handguard offer a stable, serviceable foundation for field use and component upgrades.