Geissele Super Duty Stripped Upper Receiver 5.56mm Heavy Profile 16in Barrel Carbine Length 1-7 Twist Sand. At the heart of this stripped upper is a Super Duty upper receiver that mates to a 15 in MK16 Super Modular rail via a center aligning tab removing any chance of rail rotation. This family of rails is renowned by operators for their performance and comfort. It features an in-house 16 in Manganese Phosphate coated CHF Chrome Lined barrel with a 1-7 twist rate. Specifications for Geissele Super Duty Stripped 5.56mm 16 inch Upper Receiver: Manufacturer: Geissele Caliber: 5.56mm Gas System Length: Carbine Length Barrel Twist Rate: 1-7 Muzzle Device: No Finish: Anodized Fabric/Material: Aluminum Gun Type: Rifle Gun Make: AR Platform Gun Model: AR-15 Magazine Included: No Condition: New Package Contents: Geissele Super Duty Stripped 16in 5.56mm Upper Receiver What firearm models does the manufacturer say Geissele Super Duty Stripped 5.56mm 16 inch Upper Receiver is compatible with? The manufacturer suggests that Geissele Super Duty Stripped 5.56mm 16 inch Upper Receiver is compatible with AR-15Geissele 08-660S: Super Duty Stripped Upper Receiver 5.56mm Heavy Profile 16in Barrel Carbine Length 1-7 Twist Sand