being that the ar barrels have the head-space set on the barrel extension you don't have to do a head space on it. it is a good idea to check the head space anyway if you have a 5.56 go and no go laying around.
an ar barrel is sort of like having a bolt matching AK upper assembly except that ALL 5.56 ar-15/m16s have a factory set head space. new bolts on new barrels are supposed to be interchangable--provided the barrel extension and bolt are set to the standard.
even most conversions are set to the standard --some match set ups are set "tight" on those they usually come with a bolt.
duct tape the hell out of it1--LOL!