There seem to be lots of opinions on the 'correct' way to headspace a barrel in the AK trunnion. Looking at SAAMI specs for min/max lengths the 7.62x39 cartridge is 1.245"/1.252" and the chamber is 1.252"/1.262". SAAMI specs MIN and a MAX gages for headspacing at 1.252" and 1.262" which correspond to the GO and FIELD gauges. The NO-GO spec is set by the rifle manufacturer and falls in between MIN and MAX and is rifle specific. So when one purchases a NO GO guage it can be anywhere between 1.252" and 1.262". This explains why people have difficulty checking their rifles. Since SAAMI considers it safe to have a minimum length round in a maximum length chamber the maximum safe headspace is 0.017" for the AK47. Using masking tape (or better foil tape) on the end of a round one can easily get within 0.017" so the the expensive gauges ground to within 0.0001" seem a little overkill for an AK-47.