dcralston......I think you are confusing some cup numbers with psi numbers in that example .
Gunslinger,
You are right. After rechecking the manual it does have the 280's cup pressure and then for the 7rm it shows the pressure in psi.
Just for my own info what is the difference between the two and why would a manual show the cup for one caliber and the psi for another? As a beginning handloader what would the cup # do for me.
Thanks
Many of the good load manuals will have a better explanation than what I can do , but basically
CUP numbers are obtained by the old copper crusher method , while PSI numbers are gotten by a piezeo-electric system or a strain guage . There is ROUGHLY ,( assuming we are talking about high pressure bolt rifle loads ) about 10,000 difference in the numbers of the same load between the systems , with CUP being the lower of the 2 .
But , for the most part , you cannot directly convert CUP numbers to PSI numbers .
As to why some load books show CUP for some calibers and PSI for others , I really don't know , but maybe the work was done in different labs or at different times . Many of the more obscure calibers will be listed with old data that was done years back with the copper crusher system .
To top it off , back in the day when old codgers like myself or BobinNH started loading , there was only the copper method , so the numbers were commonly quoted as simply PSI , when they were really today's CUP .
All clear as mud now ? (grin)
