Maybe Quickload's default case capacity of 72 grains h2O for the 350RM is conservative? 62grs TAC under a 225gr TSX @ 2.8" would be 114% load density, according to QL
To get 103% LD, case capacity has to be increased to 77.75grs h2O (8% increase). Maybe measure some of your fired casings to see how much water they hold. Weigh fired cases empty, fill with water to the top, and weigh again. Subtract the difference in weight to get the net h2O capacity
QL suggests only 2500ish FPS will be made with TAC w/ 225gr TSX from a 20" barrel, not sure how Barnes is getting 2764 fps. That is basically 24" 338 Win Mag velocity