doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com LITTLE SKEETERS

Is the crusher we are referring to here either a lead or copper pellet, or is only one of these used to measure shotgun pressures? Are L.U.P. and C.U.P. measurements of the same level, say for example 7500, equal in piezoelectric or p.s.i. readings, or is there a differece between those two units of pressure measurement? I guess what I'm getting at is when folks here say that a 7000 psi load is safe in a certain Damascus barrel, is this copper crusher, lead crusher, p.s.i., or what?

It is PE measured psi, the most common unit now in use. LUP (based on lead crushers) and CUP (based on copper crushers) were in near universal use before PE and strain gauges became readily available. Lead is used for lower pressures and copper for higher. The trick was to match the crusher materials compressive strength to the pressure range anticipated. If the crushed was not significantly deformed, it was difficult to measure accurately. If overly deformed, it became inaccurate. Crushers can measure only peak pressure they are exposed to; a chamber mounted crusher will measure chamber peak pressure and a barrel mounted crusher will measure barrel peak pressure. PE and strain gauge measure near instantanious and can deliver time based curves of pressure build-up and decay. Crusher pellets must be made extreamly accurately or they have no value. Used to be that cartridge loaders bought certified crusher pellets in large volume.

PE and strain gauge readings will depend on the accuracy of system calibration. Crushers depended on the accuracy of the crusher pellet and the accuracy of the measurement of deformation. Crusher and electronic psi are not in strict agreement. 2-p gave a simple and effective conversion of LUP to PE psi.

I have found removing light loads from my 10-12 Skeeters, not a problem. But the other day, I shot 2 3" magnum # 4 Buck loads using them.....Big problem took several days of soaking and application of a drift using a ball pean hammer to get them out.........

One further note on the above formula. This formula was devised in England. I have absolutely nothing to confirm it could be used for US pressures IE I have nothing to confirme a load which recorded 3 tons under the British systemn would in fact record 6720 LUP in a US pressure gun. R'Mans very good post shows the problems that could be encountered. These crusher pressure measurements served a most needed purpose in their day, but were at that time usually listed as "PSI". I do not recall for certain when the terms LUP & CUP began to be widely used, but care must be used in interpreting older pressure listings as to what was actually meant. Actual true PSI will always be equal to or higher than a crusher pressure, never lower.