Had some similiar results with AA 2520 and their QC was so bad that I've avowed since the mid 90s to never purchase another AA powder if I can avoid it..
Totally SAFE loads at around 80. But we got into a match at around 100 plus some horrendous humidity, no breeze, almost killer weather in the pines of E Texas in a regional match once.... Kayla(my adopted junior shooter) shot the first few at 600 and was NAILING the center, but blowing primers so I grabbed all of her ammo, and opened my water jug with ice and water left, and dumped em all to the bottom, handed em to her one at a time as needed after wiping them off, she won the leg match that way....
I keep all my ammo in the heat, in a cooler with no ice or heat, just protects it better in the summer.
27.0 was a locally famous load for 52s here too, and got its owner Arnold Granger, in deep a few times in the heat... say isn't 748 the same as one of the surplus powders? BLC2 or some such, I can't recall...
