CMMG MkG .45 ACP Banshee Fixed Ejection Upper Group Receiver 5in 1-16 Twist 0.578x28 TPI .750in Midnight Bronze. Compact action RDB was an advancement to the original RDB. This (fixed ejector on RDB) is a continued advancement bringing new technologies to the original platform. Chambered in one of the most iconic calibers with over a century of faithful use the 5 BANSHEE MkG upper group in 45 ACP is the shortest MkG upper CMMG offers. Ready to pair out of the box with an existing or new MkG lower group this upper is the piece you need to build the ultimate fun-sized AR pistol or SBR. Specifications for CMMG MkG .45 ACP Banshee Fixed Ejection Upper Group Receiver: Manufacturer: CMMG Caliber: .45 ACP Barrel Twist Rate: 1-16 Threads per Inch: .578x28 Muzzle Device: CMMG Zeroed Muzzle Brake Finish: Cerakote Fabric/Material: Aluminum Gas Block Journal Size-Diameter: .750 in Gun Rail: M-LOK Barrel Material: 4140 Chrome Moly Vanadium Magazine Included: No Package Contents: CMMG MkG .45 ACP Banshee Fixed Ejection Upper Group Receiver CMMG 45B570F-MB: MkG .45 ACP Banshee Fixed Ejection Upper Group Receiver 5in 1-16 Twist 0.578x28 TPI .750in Midnight Bronze