AIM Sports Inc Complete AR Pistol Kit Pistol Length Gas 300 Blk 10.5in Black Large Black Large. 300 Blackout Pistol build kit comes with just about everything you need to complete your pistol or SBR build. The kit features all the necessary components to get your build going just add your stripped lower receiver. Specifications for AIM Sports Inc Complete AR-15 .300 Blk 10.5in Upper Receiver Pistol Kit: Manufacturer: AIM Sports Inc Caliber: .300 AAC Blackout Barrel Length: 10.5 in Color: Black Package Contents: AIM Sports Inc Complete AR-15 .300 Blk 10.5in Upper Receiver Pistol Kit AIM Sports Inc AR5CUB13: Complete AR Pistol Kit Pistol Length Gas 300 Blk 10.5in Black Large AR5CUB13 Black Large