Rock River Arms Completed Upper Receiver A4 .450 Bushmaster 20 Inch Barrel 1-24 Twist 5/8-32 Thread Free-Float Handguard Brake Black. 450 Bushmaster Completed Upper then you have come to the right spot.. Established working with several of the most extremely robust and long lasting substances around these AR15 Upper Receivers by Rock River Arms offers you an item which gives you many years of stability. Rock River Arms has been making superior quality products for a number of years and the Rock River Arms A4 .450 Bushmaster Completed Upper is their particular way of demonstrating just how much they care. Right here at OpticsPlanet we ensure that it is our obligation to obtain the perfect product for your needs and featuring the Rock River Arms A4 .450 Bushmaster Completed Upper is something that we're delighted to offer. Specifications for Rock River Arms A4 .450 Bushmaster Completed Upper: Manufacturer: Rock River Arms Caliber: .450 Bushmaster Barrel Profile: Standard Gas System Length: Mid Length Barrel Twist Rate: 1-24 Threads per Inch: 5/8x32 Handguard Type: Free-Float Muzzle Device: Brake Finish: Anadized Color: Black Gas Block Journal Size-Diameter: .936 in Gun Rail: Full Top Rail Condition: New Barrel Material: 416R Stainless Steel Bolt Carrier Group Included: COM-SPEC Magazine Included: Yes Mount Type: M-LOK Package Contents: Rock River Arms A4 .450 Bushmaster Completed Upper Bolt Carrier Group Charging Handle Assembly 5 Round Magazine Rock River Arms 450B0587: Completed Upper Receiver A4 .450 Bushmaster 20 Inch Barrel 1-24 Twist 5/8-32 Thread Free-Float Handguard Brake Black