RL-15 works just fine. Gives excellent velocity and good consistency (plus tight groups).
I first tried BL-C(2) but didn't see great results. However that was when the barrel was new and the gun seemed to do poorly even with factory ammo. Now the gun seems easy-to-load-for, so maybe I'll go back to BL-C(2).
I've tried RL-19 with a heavy 280 grain bullet and got decent results. They didn't exceed RL-15 velocities, but higher velocity wasn't what I was hoping for. I wanted a forgiving load. Meaning one I could just scoop-n-dump the powder charges and still be well within the margins of safety.
I'd also wonder about H414 and one or two of the other powders that seem to perform really well in the .338-06. It seems like the powder companies cooked up some loads for the Whelen. Then later cooked up .338-06 loads using entirely different powders. I don't understand why there isn't more overlap.