If I recall I used 100 grs of H-4350 with the 350 gr X, and 102 grs was the maximum listed in the manual. I used the same data with the Speer 350 gr Magtip, and velocity was the same for both bullets in my rifle - about 2800 fps which I believe is higher than the claimed velocity in the manuals. I am sure you won't have any issues with the TSX version of the X bullet, but start at 95 grs and work your way up a grain at a time.