View Full Version : Copper Units of Pressure in Lyman
Looking through the load data for the 175 grain lead bullet in the Lyman manual the max loadings list pressures ranging from 28,100 cup to 29,000 cup. I would like to know what percentage of the maximum these loadings give. Does anyone know what the maximum pressure rating for the 10mm is in cup? If cup and psi are roughly equivalent in this range it seems strange that the max loads listed generate more than 6000 psi less than the maximum pressure.
If you read data on the two measurements they do not directly correlate to each other...30,000 CUP doesn't equal 30,000PSI. There have been people who have tried to put together charts but were unsucessful.
Also be aware that the strain gauge methods differ, those used by SAAMI are usually internal to the chamber others are being calibrated on the outside of the barrels.
Because the CUP and PSI measurement methods are so different, there is no direct conversion between them.
see page 72
(its a good read, go through the whole book!)
For pressures below about 30,000 the two pressure
scales are virtually identical (at these lower pressures, the pellet doesn't change much and it doesn't take very long for it to achieve its new conformation).
Between 30,000 and 40,000, the CUP scale starts to lag behind the psi scale,
and above 40,000 the two scales start to differ significantly (60,000 psi
corresponds to roughly 50,000 CUP and 100,000 psi corresponds to about
70,000 CUP). There is a calibration curve correlating the psi and CUP pressure
scales in "Firearms Pressure Factors" published by Wolfe Press (this is an
excellent book, and is recommended for anyone who handloads ammunition).
Thanks for the link gofastman, this is just the info i've been searching for.
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