Geissele Super Duty Stripped Upper Receiver 5.56mm 16.5in Barrel Carbine Length 1-7 Twist Sand 16in. 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 5.56mm Super Duty Stripped Upper Receiver 16in: Manufacturer: Geissele Caliber: 5.56mm Barrel Length: 16.5 in 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 Condition: New Magazine Included: No Package Contents: Geissele Super Duty Stripped 16in 5.56mm Upper Receiver What firearm models does the manufacturer say Geissele 5.56mm Super Duty Stripped Upper Receiver 16in is compatible with? The manufacturer suggests that Geissele 5.56mm Super Duty Stripped Upper Receiver 16in is compatible with AR-15Geissele 08-247S: Super Duty Stripped Upper Receiver 5.56mm 16.5in Barrel Carbine Length 1-7 Twist Sand 16in