2.5 or 3% makes very little difference, still ~7% SB - way too much. No need for the BO, HT them after cooking for an hour, drop in ice water. I use 4% Sb HT & PC in 308W, no problem. Just add a few nuggets of superhard and some shot for arsenic to the isocore for the alloy.
Same alloy for BO 145gr pushed hard. GC and only in the 17-1800 fps range, AC isocore should work good.