Vague title but wanted to get attention because I had an event that I can't find an answer for and need your brains to figure out my fail. I was sighting in my 1981 BAR 7mm RM shooting my deer loads: 140grain Nosler balistic tips RP cases trimmed to 2.490 2nd reload Small base sized [because of BAR] on first reload but FL on second) CCI 250 LRMP 64.1grain of IMR 4350 First mag (3 rounds) it was darts, ZERO signs of problems and spot on waited 30 minutes while others shot and attempted second mag, I tried to run some of my first elk loads and had FTF on all attempts, after looking at the scrapes on the ogive (and later buying a gauge) I realized my OAL was too long for that bullet tip 175 seirra GK and the bullet would not reach its band and properly headspace... thus the failure to fire. after trying to get the elk mag to run I put in another mag of the deer loads. this is where the problem came in. The first round fired great, but the second round sounded and felt off and did not hit the target at all. I dropped the mag and ejected the next round and didnt see any issues nor in cycling the action did I feel any problems. I reloaded the final round into the mag and loaded the weapon.. shot great on point but popped the primer out of the case. I picked up the cases and on the first there was no issue, the second I actually pierced the primer cup (I know I should have looked immediately after noticing an abnormality) and the third the loose spent primer looked normal aside from being removed from its home. I am VERY confident in my reloading consistency particularly with this batch as I got a new trimmer and measured every step meticulously, all of the cases looked fine with no other signs of over pressure. what did I screw up?