I'd take a hard look at 330 Dakota data.
I just checked on line and Norma's data for the 338 Norma calls for a max charge of 88 gr MRP for a velocity of 2916 fps. with the 250 Sierra.
For the 330 Dakota, the Hornady manual calls for a max charge of 82.3 gr of RL22,and 83 gr of H4831 with the 250 gr Hornady bullets.Both these powders are in the same burn rate as MRP,even if not exactly the same.
The two cases are roughly the same case length. I am thinking a guy could take starting loads for the 330 Dakota and work up. Of course proceed with caution!
Of course an easier way is to check Norma's data for the cartridge and go from there.
