I need some full power 458 lott loads using IMR-4320.Need
around 2350-2400 fps with 500 gr sp.

85.0 grains is max with the 500 grain bullet. Probably start around 79 or 80 and work your way up. 85 should get you well over 2400 fps.

Most Lotts will work well with 84 grs. and that has become standard, but I have had a few that would handle 85 to 86, but they were long in the throat and they got some sizzleing velocities...

I use the woodleigh 500 gr soft with 81 gr of AR2208 which is the Aussie equiv. of your powder (I think). I use a Hornady case and fed 215m primer. The woodleigh bullets are excellent.

Rick,
DUDE... max loads vary per gun... start with the book and work up over a chrono graph

jeffe