The Geissele Super Duty® Upper (Stripped) features the quality and workmanship you've come to expect from the Geissele name. The Super Duty upper receiver mates to a 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 Manganese Phosphate coated, CHF, Chrome Lined barrel with a 1-7 twist rate. Our barrels are precision machined and cold hammer forged at our state of the art facility in North Wales, PA; utilizing the highest quality materials available.