74.0 of IMR 4320 provides about the same data as Varget below using 400s (but I haven't tested its accuracy on the Chatfield-Taylor. I think the 350 TTSX would work well in the US for your purposes (and I see they were getting 2500ish fps out of it. A little faster, a little flatter, but you may just wish to consider pleasant-shooting 400 gr NPs at the factory V of 2,350 fps. (Cranking it up to 2,450 was for elephant and even 2,550 is possible, but punishing in most rifles! It's higher pressure than the Rigby, et. al. so that translates into more felt recoil. ) IMR are my favorite plowders, but there are typically better choices nowadays, especially for larger cases.) 'Did extensive handloading/testing when I got mine years back. In the end, Varget was selected (<1" groups for the best DG hunting bullets: Swift A-Frame and Barnes Banded Solids (the solids printed the same but went 10 fps faster using the same load.) The Nos PT (400s) shot Mickey Mouse groups-super accurate, but I decided to go w/ the A-Frames for Africa.) The 1st load using the 300 gr wasn't my load, and I saw some others that yielded 2,650 fps (which is more like it for a 100 gr lighter bullet.) If you're looking for max. velocity in the (458 WM) case, using the more dense dual-bases like A-A, Ramshot, Western (all the same co.) and TAC/Xterminator/AA-2XXX series are all exceedingly similar. Though I managed to wring 2,500+ fps using TAC, it was pretty brutal to shoot and not quite as accurate, so 'went back to Varget. My custom M70 is 21" or 22", 11 lbs magnaported w/ 2 Hg reducers in the stock. GL!