I thought when you said "built" I assumed you assembled all the parts from a stripped receiver. Putting a assembled lower with a assembled upper together is just what I did. But I do not classify that as me building it. I just put the 2 parts together. Just a misunderstanding.I never experienced any "over gassing" that I know of, I actually don't even know what that means. When I built it, I bought a standard collapsible carbine buttstock with whatever buffer and spring that it came with.