Filing serial number off is generally unsuccessful as a means of rendering a firearm untraceable. Law enforcement can use a variety of methods to reveal the ser

Filing serial number off is generally unsuccessful as a means of rendering a firearm untraceable. Law enforcement can use a variety of methods to reveal the serial number due to the changes that the original stamping makes in the metal underneath the actual surface impression. While in theory using an impact tool or a milling type tool could work to remove the underlying metal there is a risk that the integrity of the part (in this case the lower receiver) could be compromised. I would take exception to the author's statement that the lower receiver is the primary firing mechanism. While it does contain the trigger and sear the upper receiver contains the full bolt assembly, firing pin, and gas system (or piston if you feel like getting fancy). My biggest question is that if they are creating lowers from billet and other parts as well, why they just don't equip these weapons with auto sears and make them full auto. Go big or go home, right?