I think the differences in the chambers is really the major point of concern.
I saw an awful lot of information today which I had not seen before. One reason is that I used "EPVAT 5.56" as a search term instead of what I had done in the past.
Unfortunately there are a lot of resources out there which make assertions that are at variance with what I would consider the most authoritative sources, which would be documents from agencies within DoD.
One thing that has complicated comprehension of all the info out there is that there was a time when pressure measurements we now refer to as "c.u.p." were once commonly referred to as "p.s.i." I have not been able to ascertain just exactly when the US-made 5.56 ammo began to be evaluated by the SCATP standard. There are several DoD originated documents available on line referring to the pressures of M193 and M855 ammo as being 52,000 psi, but there are others that quote 55,000 psi. I believe that the former are copper-crusher numbers and the latter are piezo measurements.
Some information flatly states that the EPVAT standards include pressure measurement identical to the CIP method but also incorporate additional performance criteria. The same is said about the SCATP standards vis-a-vis the SAAMI pressure measurement methodology.
It's a tangled web, to say the least.
