The Tactical Machining 80% TM-22 receiver starts as a billet of 6061 aluminum. The profile is fully machined leaving a picatinny rail on top for attaching your favorite optic. The picatinny rail also serves as the attachment point when being used with our jigs. This is a great home hobbyist project and we do not recommend the use of a mill like our 80% AR-15 lower receivers. We recommend using a drill press for the project. The remaining operations of this receiver are as follows: Drill Barrel Hole Drill and Tap Barrel Clamp holes Drill Bolt Stop Drill Trigger Assembly holes Drill and Tap Stock retention hole While the tasks are easier to complete with the 80% TM-22 it is extremely critical that the jig and your drill press is level. Do not remove the jig in between operations on the side you're currently working from. This is especially important for the barrel & barrel clamp holes. They must be precisely placed. Also, do not drill all the way through the receiver on the bolt stop & trigger assembly, these are required to be flipped as the drill will walk.