I am just now working up loads for my DTA .338LM. So far Retumbo Power has done the best grouping. IMR7828 not as good.
Using 250gr Sierra HPBT (2nd best) & Spitzer BT. Hornady 250 RN (3rd best) 250Gr SP interloc and 225gr SP interloc. Nosler 225GR AccuBond (1st). I have some 300Gr Senars...