Geissele Super Duty Stripped Upper Receiver 5.56mm 11.5in Barrel Carbine Length 1-7 Twist Sand 11.5in. At the heart of this stripped upper is a Super Duty upper receiver that mates to a 10.5" 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 11.5" Manganese Phosphate coated CHF Chrome Lined barrel with a 1-7 twist rate Specifications for Geissele Super Duty Stripped 11.5in 5.56mm Upper Receiver: Manufacturer: Geissele Caliber: 5.56mm Barrel Length: 11.5 in Gas System Length: Carbine Length Barrel Twist Rate: 1-7 Muzzle Device: No Fabric/Material: Aluminum Gun Type: Rifle Gun Make: AR Platform Gun Model: AR-15 Condition: New Magazine Included: No Charging Handle Included: No Package Contents: Geissele Super Duty Stripped 11.5in 5.56mm Upper Receiver What firearm models does the manufacturer say Geissele Super Duty Stripped 11.5in 5.56mm Upper Receiver is compatible with? The manufacturer suggests that Geissele Super Duty Stripped 11.5in 5.56mm Upper Receiver is compatible with AR-15Geissele 08-245S: Super Duty Stripped Upper Receiver 5.56mm 11.5in Barrel Carbine Length 1-7 Twist Sand 11.5in