GEISSELE AR-15 SUPER DUTY STRIPPED UPPER RECEIVERS 5.56MM The Geissele Super Duty Upper (Stripped) features the quality and worksmanship you've come to expect from the Geissele name. At the heart of this stripped upper is a Super Duty upper receiver that 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. Featuring an in-house Mag Phosphated, CHF, Chrome Lined barrel with a 1-7 twist rate. Geissele barrels are precision machined and cold hammer forged at their state of the art facility in North Wales, PA; utilizin Mfg: Geissele Automatics