This Rock River Arms RRA 450B0461 half upper is configured for the .450 Bushmaster and built around a forged A4 upper receiver with a mid-length gas system. It uses a 16-inch stainless steel heavy barrel with a 1:24 twist that has been cryogenically treated, and is finished with an RRA Operator Brake threaded 5/8-32. The unit ships complete with a 13-inch extended lightweight free-float M-LOK handguard and includes a bolt carrier group, charging handle, and one 5-round magazine.
Key Specifications
- Chambered in .450 Bushmaster as specified by manufacturer data.
- Upper receiver type is a forged A4 configuration.
- The barrel measures 16 inches and is described as heavy profile.
- Barrel material and finish are stainless steel with cryogenic treatment.
- The barrel twist rate is 1:24.
- Muzzle device is the RRA Operator Brake with 5/8-32 threading.
- Gas system is a mid-length setup with a low-profile gas block.
- Handguard is a 13-inch extended lightweight free-float rail compatible with M-LOK accessories.
- Includes a bolt carrier group, charging handle assembly, and one 5-round magazine.
This upper is designed for shooters who need a robust .450 Bushmaster configuration on a mid-length AR platform. Its stainless heavy barrel and free-float M-LOK handguard make it well suited for field use where reliable function and straightforward maintenance are priorities. The included bolt carrier group and charging handle make it a practical choice for assembling a complete upper quickly.
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