Rock River Arms | 450B0461 | .450 Bushmaster A4 Upper | 16in SS

The Rock River Arms .450 Bushmaster complete upper (MPN 450B0461) is designed for AR-platform large-bore builds and conversions. It features a 16in cryogenically treated stainless steel barrel with a 1:24 twist and an RRA Operator brake threaded 5/8-32. The assembly includes a forged A4 upper receiver and a 13in free-float M-LOK handguard and ships with a bolt carrier group, charging handle, and one 5-round magazine. This upper is suited to field use in hunting and medium- to long-range big-bore applications.

Product Specifications

• The manufacturer is Rock River Arms.
• The manufacturer part number is 450B0461.
• The product type is a complete upper assembly.
• The caliber is .450 Bushmaster.
• The upper receiver is a forged A4 design.
• The barrel measures 16 inches and is stainless steel.
• The barrel has a 1:24 rate of twist.
• The barrel was cryogenically treated.
• The muzzle device is an RRA Operator Brake threaded 5/8-32.
• The gas system is mid-length with a low-profile gas block.
• The handguard is a 13 inch extended lightweight free-float rail that is M-LOK compatible.
• The handguard finish is black.
• The overall finish type is black.
• The assembly includes a bolt carrier group, charging handle, and one 5 round magazine.
• The UPC is 842834124138.

Whether assembling a dedicated .450 Bushmaster hunting rifle or upgrading an AR-platform for large-bore field performance, this upper delivers a complete, specification-driven package with durable stainless components and modern accessory compatibility.