Fishslayer
Member
One more time.
Do you notice a big difference between lead and jacketed bullets? Do you notice a big difference with 5 grains more bullet weight? Do you think a starting load for a 135 grain jacketed bullet would be extreme overpressure with a 140 grain lead bullet?
Upon inspection of the blown out case I would suspect the answer to at least one of those questions would be "yes." Possibly a combination of factors combined with a lead bullet with too long OAL stuck in the rifling.
So far the best idea you've come up with is going to a slower powder.
Fast powder, high pressure cartridges, lead boolits and cobbled up data.... YIKES!