I've loaded and had good results with both IMR4350 and IMR4831 shooting Speer SP 200 gr and Horn Spire Pt 225 in the .338 Win Mag. I have used IMR4831 more.
From my notes of 225 Horn SP and IMR4831: "Took cow elk Approx 200 yds. Broadside facing left-entered high left leg-no bone hit, broke rib going in-totaled both lungs-broke rib off side-broke upper leg on off side-contained w/in hide off side. Wt. 148.6 gr for 66.6% weight ret. Dia .594" for 1.76% dia expansion" She kicked off at the shot and was dead when she hit the ground. Like Thor hit her with his hammer. I was slightly above her when I shot.
For several reasons I've been buying and shooting more Horn. bullets lately and have been playing with the .375Ruger. On those mono bullets (CX) you have to watch the impact speed. Horn. says it should be at least 2000fps. The way I load for it, that would exclude a 400 yard shot. My plan is to work up a pair of loads; 250 CX up to 300 yards and 270 Interlocks for beyond 300 yards, if I can get them to print right, just in case I have to shoot that far (stopping a wounded animal from getting away.)
This is a cast boolit site! I bought a mold for the .375R and will be making lead bullets for plinking instead of buying the "cheap" jword bullets.
Good luck OP. I like the .338WM!