If your going to build an AR start with a 100% receiver unless you have a mill and some metal working skills or mad skillz with hand tools. I assembled a few 100% lowers then did an 80%, followed by a forging that someone EDMed out the magwell. I am now starting on a 0% forging. Unless you really just like to make chips with the mill. I would recommend just buying one. I have never paid more than 130 out the door at a gunshow for a DPMS lower.