Hi, I am building an AR-15 from ground up. It is more along the lines of a budget build though. The barrel is AR-Stoner/ESS from Midwayusa.com and the bolt is PSA M-16 Full auto MPI mil spec. My question is, do I need to do a head space check with the barrel and bolt combination? I hear some people don't as the barrel extension already sets the head space. If I need to check it, is this easier to do before the barrel is installed or after? If I need to check it, any place local to rent Go/No Go gauges? What have you builders done? Thanks.