```From: Norman Johnson Newsgroups: rec.guns Subject: re: Can someone provide a definition for a "Copper Unit of Date: 3 Sep 1999 22:49:50 -0400 #Can someone provide a definition for a "Copper Unit of Pressure"? #I've been trying to find out exactly what this is, in terms of PSI of #Pascals, and can't find anything. # #All I found was the revelation "unit of pressure, dervived from #crushing a copper cylinder" on a miliary website somewhere. The process is such that there is no conversion from one to the other. The CUP method uses a "standard" copper slug that is compressed according to the pressure CURVE of the tested round. It is a reliable way to control ammo pressures because it is repeatable within the limits that must be maintained to manufacture safe ammunition. As you may know, this is very roughly equivalent to psi but not close enough to assume that they are the same. To do so would be foolhardy. I will attempt to explain why. Strain gages are used to measure pressure in psi. The PEAK value is that which is published but the whole pressure curve is revealed on the oscilloscope. Herein lies the inconsistency of the two methods. Lets see if I can explain that inconsistency. Assume two pressure curves having the SAME AREA UNDER THEIR RESPECTIVE CURVES, one with a SPIKED (high "Q") pressure curve, the other with a FLATTER (low "Q") curve. Because the pressures are such that the copper slug is in plastic deformation, the area under the curve is associated with the slug deformation. Sort of like punching a block of modeling clay with your fist versus holding your fist against that block with the same force for an extended period. A strain gage would indicate a higher pressure for the spiked curve and a lower pressure for the flatter curve while the copper slug might have the same deformation and thus indicate the same CUP measurement for the two loads. In summary: Two loads having the same area under the pressure curve might show similar or same CUP measurements, while the one with the sharp spike would show significantly higher pressure (psi) using the strain gage. Clear as mud? They both work - but one does not translate to the other. Because there is much more information made available by use of the strain gage, and because it is far less time consuming, it is slowly replacing the copper deformation method. God Bless! Norm ```