"and how far did they drift apart with the advent of more modern powders?"
This is something we can probably sort out with personal experience. I haven't loaded for the 300 Savage, but I've doted on the 30-06 for decades. With my handloads, all from mainstream loading manuals with the 24" barrel:
200 gr @ 2600 fps (and probably up to 2700 fps)
180 gr @ 2800 fps
165 gr @ 2940 fps
Those are all from my 24" Remington 700 with "book" loads.
I have no recent experience with the 150's and the 30-06 cartridge.
Regards, Guy
