Rembo,
I have a #1 and an M77 both in .458 Win Mag and they both shoot nicely with the following load that duplicates heavy 45-70 loads...
400gr/405gr JFP over 67.0gr IMR-4064/CCI200/W-W cases
This loading gives me 1915fps in my guns and shoots 1" at 50 yards easily. It's a very pleasant load and a fun plinker yet packs plenty of wallop for nearly all North American big game as-is.
I've found the .458 Win Mag to be very easy to load for and alot of fun.
