Spike Camp

Is there a formula to calculate pressure ? ( cup)

Is there a formula to calculate pressure ? ( cup)
« on: September 10, 2017, 08:16:24 PM »
I was testing some loads today in my 300 and 340 weatherbys. And velocity readings were on the high side. I dont trust my chronograph. But the 84.5 grs. Of IMR 7828 were at 3300 fps and one case sort of stuck for a second. I never had that problem before with that load. But I would like to know what the cup is with that load and a 180 gr. Nos. Balistic tip. The load was being tested against norma MRP and was Slighty faster. Which it shouldnt be.
3 shot avg. With MRP was 3297
3 shot avg. with IMR 7828 was 3300
Dosent make sence.


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Re: Is there a formula to calculate pressure ? ( cup)
« Reply #1 on: September 11, 2017, 09:18:32 AM »
The short reply is no.   crusher guns (cup/lup)  vs transducers (psi) are open to the quality of the test and conditions (good working order) of all test equipment and the ballistic tech's interpretation of the findings.  There is a strain guage out there for the not so novice reloaders if they wanted to read pressures on an (individual firearm ).  How accurate it is as compared to the other two methods which are based on the ammo vs  the strain guage based on ammo & firearm.  This is just general info people can get into trouble when trying to compare powder burn rates thinking OH !  the other powders are only one up or down on the burn rate chart  from the original powder so it should be fine ?   WRONG !!! answer.  These powders are tested and re-tested using one of the approved methods.  Each caliber is different ,  and has to be treated as such in any pressure test, different size, different case capacity, different, bore, different bullet weight, different gun, etc.  My own personal view velocity readings are secondary in importance  vs accuracy which is most important,  SO LONG as the velocities are not hundreds of fps apart, in that case I would start looking at different things to bring velocities back up to somewhat accepted velocities.  All guns are different  so I don't expect to always get highest velocities with best accuracies.