I have a M-70 in 375 AI, I used RL-17 to power 270 gr TSX's to 3100 fps looking for excessive pressure, never found it and suspended experiment at that level, backed them down to an even 3000 fps, accuracy is a bit over an inch for 3 at 100 yards.
Your friend can start at 83 grs of RL-17 and work up if you wish, that will start you in the neighborhood of 375 H&H performance.
Gunner
