Case Capacity

People always ask about differences in case capacity between commercial and military brass, so many don’t even think about the difference between different headstamps of commercial brass. The other day I was loading some 250 savage in Jamison brass with Hunter powder. I was 2gr under max and when I lifted the funnel off the case, powder spilled everywhere. After thinking for a bit I tried it in RP brass and had room to spare.
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There is substantial difference in capacity between these two brands of brass. I decided to do a little test with Winchester Staball Match and the two different headstamps. I chose that powder because I could fit a max charge on both cases. I loaded 7 rounds with each, going up .5gr in charge weight from almost minimum to maximum. The results were as I expected but was fun to have the actual differences in actual numbers to compare.
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At starting charge there was 102fps difference. Midway was 170fps difference, and at max there was 139fps difference.


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100 fps is factory data for a case step in caliber with like pressure........
It's also why up to 165 gr the 308 is in a dead heat with the 06' .......
It takes roughly 5,000 psi or 5 gr of most powders to get it in a 30 cal .

2800 fps in a 25 cal 115/117 is nominal in deference data for the 93/95 Mauser in 257 Roberts and start loads in the 25-06' . It probably won't hurt a 99 but it will be hard on the pre war Savage bolt guns and Spanish Mausers.

Good information and data .

I’m shooting in a Ruger M77 MK2, so I wasn’t worried about the pressure in my rifle, but it absolutely could reek havoc on older firearms. I didn’t measure case head expansion as I didn’t see it relevant because of the gun I was using, but there was a very noticeable increase in recoil when firing the rounds in Jamison brass.


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