Marco, you can get the information straight from the horse's mouth. Call Lake City Army Ammo Plant in Lake City, Missouri then ask them when the switched from copper crusher gage systems to peizo or transducer ones. Then ask them why the specs state one way and they did the other.
Mehavey, 55,000 cup is about the same as 62,000 psi in 22 caliber bores the way military systems spec'd the way it's measured.
And yes, the entire world of printed pages on this is typically contaminated with misinformation. It ain't all the fault of the writer. It's the lackadaisical way the language and terms were used between the ballistic engineer who did the pressure testing and all those between that person and the likes of you guys and me.
After a discussion of CUP and PSI with a ballistics engineer at the Lake City Army Ammo Plant in the early 1970 I pretty well understood all of this, but I sometimes misuse/mix-up the terms myself. It wasn't really a problem until the 7.62 NATO round hit the military streets and the .308 Win. round hit the civilian ones. Prior to that everyone pretty much talked PSI and the pressure tests were all made with CUP systems. About the time the .308 Win. came out, piezo and transducer pressure systems were starting to be used. Their PSI numbers with the same load specs and test barrel specs were higher than the CUP numbers. And the rest is history, a confusing history at that.
Last edited by Bart B.; November 20, 2012 at 12:23 AM.