Hey Odette, my barrel slugs at .4585 so I size to .460.
I use standard length cases and give my Hornady cases to a buddy who loads those XTP bullets.
**** USE THIS INFORMATION AT YOUR OWN RISK *****
I crimp on the crimp groove and my COL is: 2.500" With that 350 grain boolit, my H335 load is 54 grain. This is because I wanted it to be around 1900 fps as that is plenty of power and has a good thump but it is not a shoulder breaker. 54 grains of H335 gets me about 1920 fps and is accurate. According to Quckload, that puts the pressure at 28663 PSI and says it should be 1848 fps. For me, I won't go above this because that same boolit at above about 2000 fps is no longer fun to shoot.
I would recommend that you start lower and see how your rifle shoots that boolit. H335 is very fine ball powder and seems to burn well even at lower pressures.
With this powder, it does pressure spike pretty quickly when it starts. I was shooting it under a NOE 460-396 RF and every 1 grain increment was pushing that boolit about 20 fps faster. UNTIL I got to a certain point and it went 200 fps faster with a 1 grain increment... That particular round (I shot 3 to make sure of the FPS) leaded the bejabbers out of my barrel... SO - keep that in mind with H335.