Alexander Arms AR15 Stripped Rifle Upper .50 Beowulf 16 in Barrel Carbine Length 1-20 Twist 49/64x20 Thread Thread Protector Black. The Upper Receiver Built Kit comes with all the key components making it an excellent choice for a home build. Specifications for Alexander Arms .50 Beowulf Upper Receiver Build Kit: Manufacturer: Alexander Arms Caliber: .50 Beowulf Gas System Length: Carbine Length Barrel Twist Rate: 1-20 Threads per Inch: 49/64x20 Muzzle Device: Thread Protector Color: Black Gun Type: Rifle Gun Make: AR Platform Gun Model: AR-15 Included Accessories: 7 RD Magazine Condition: New Magazine Included: Yes Features of Alexander Arms AR15 Stripped Pistol Upper Thread Protector Complete upper receiver Charging Handle Gas block Dowel pins Gas tube Complete BCG with bolt One 7 Round Magazine Package Contents: Alexander Arms .50 Beowulf Upper Receiver Build Kit 12" or 16" Barrel 1:20 Twist Rate 49/64-20RH Threading Thread Protector Included (Upgrade Options Below) Includes complete upper receiver Charging Handle Gas block Dowel pins Gas tube Complete BCG with bolt One 7 Round Magazine What firearm models does the manufacturer say Alexander Arms .50 Beowulf Upper Receiver Build Kit is compatible with? The manufacturer says that Alexander Arms .50 Beowulf Upper Receiver Build Kit is compatible with AR-15Alexander Arms KIT-50: AR15 Stripped Rifle Upper .50 Beowulf 16 in Barrel Carbine Length 1-20 Twist 49/64x20 Thread Thread Protector Black