coyote wacker wrote:Would say your brass is a little too short or chamber is a little long....
I have a 50 B&M Super Short have a lot of some brass that has been shot 20 times and counting and also know several people with them....all loads pushing 60'000 psi....it is basically like the 450 BM straight case no shoulder 1.65" long rebated rim...I've never had a problem like the 450 BM were brass gets shorter is it is fired....I think the problem is lower pressure in the 450 BM allowing the neck to get pushed forward on firing....it also could be Winchester 70 CRF on the 50 B&M SS not allowing brass to move when firing....
Have one lot 450 BM brass that have been fired 4 times at close to 60'000 psi in a bolt action only and it is still OK not getting shorter nor need to be trimmed....
You're right in that the 450b needs more pressure than SAAMI spec to lock the case in place inside the chamber. The lower pressure as you surmised, allows the case to shorten a little with each successive firing. Holding my loads to 38k PSI
or less renders them too short after as little as four loadings. At least that's been my experience with my AR platform. Starline brass, being a little harder than Hornady, resists shortening a few more loadings. In bolt rifles, where higher pressures are less of a risk, the case should lock in pretty well and hold its length. If you experience cases getting longer, you're treading on thin ice. that extra brass comes from somewhere.
Hoot
FWIW, this is the first time that I've heard of the 50 B&M Super Short. Pretty cool IMHO!