Ah, yes, the .416 Taylor carried the mail for Sir Spruce with a 325-gr X-Bullet at 2600 fps, sectional density of 0.268, very much like a .458-400gr with SD = 0.272.
Little bigger hole with the .458-400gr so maybe we could get by with 2400 to 2600 fps MV in the SAAMI .458 WM and .458 WM+ ? This will require use of monometals like the X-Bullet. Maybe someday a .458-400gr brass hexploder ?
400-gr solids at 2600 fps might gain stability from their shortness. I guess a 400-gr round-nosed solid might stay straight for greater depth of penetration than a 500-grain round-nosed solid, but that ain't saying much. Could a higher velocity .458-400gr FN or HYDRO keep up with a heavier and slower .458-caliber FN solid ? Probably. As Sir John suggested, adequate for elephant.
Sir Ron as I see it Mono metal expanding and solids have changed the rules
I got banned on another web site for a debate that happened on this site. That's a first
