I just joined the fray also. I have a fair bit of experience with hunting loads for the 338 RUM, so kind of started off their with the edge. Its a customers rifle. 30" barrel in a chasis. I've only ladder tested looking for velocity range. I started with h1000 and retumbo under 300 berger hybrid target. Retumbo looked better initially. Last session I ran up to 97 grains and had 2970fps. Seating out to 3.940 which is .025 off the lands. Next session will shoot for groups and ES. Encouraging enough, in the last ladder, the final 4 shots had 1 grain differences each, and formed one ragged hole.
I'll report back as I go.