Re: 24" 338 RUM velocities? advice needed
I can't tell you what you will get with your 338 RUM. Can mention my experience though. I built a 24" 300 RUM for the 230 gr hybrid and am using RL-33. Most accurate load is 100 gr with the 230 going 2975 fps. I think you will do even better with the larger bore.
If you read Kirby Allen's thread where he used RL-33 he got his best results with lowest ES using heavy bullets into the rifling. I would bet money your 338 RUM will surprise you with the 300 gr bullet.
Alliant has load data for both weight bullets you want to shoot and with a 24" barrel!
300 gr sierra OAL 3.59" 99.3 gr for 2718 FPS.
250 gr sierra OAL 3.59" 106 gr for 2988 FPS