As you probably know, you can't just take a bullet of the same weight and load to a max PSI.
Going back and rereading my OP, I see I overstated that I fired ALL of the 50 standard barrel reloads and it can be calculated that 25 primers blew out. That is
not what I did.
After 6 primer blowouts at 12% below maximum (in charge weight of 15.0, 15.1, 15.3, and 15.4 grains ONLY), I QUIT that string of 3-shot tests in the Standard barrel and fired, watching for signs of increasing pressure, all 48 rounds, in 3-shot groups in the Bull Barrel (15.0 through 16.5 grains in 0.10 grain increments) staying below the maximum load of 17.0 grains (as the 60 grain Nosler Partition is not the aforementioned 55 grain Hornady bullet). I could have/should have stopped at 15.2 grains in the Bull Barrel because the 3 shots were practically on top of one another at 100 yards
tempting me to use IMR 4227 in that rifle to that weight charge - but I WON'T.
Thanks to all for your concern and reasoned opinions. I cherish ALL of my extremities and hear you LOUD and CLEAR. In the trash these cases go. Back to the books to find a suitable powder alternative.