So I set up a 458 winmag barrel, but for now for the most part I want to load a 300 gr bullet at about
2000-2200 fps. The heavy stuff will come later.

I can load a slow bulky powder like H4895, and get an 80% burn, almost complete fill and a huge fireball.

I could also load a faster powder like imr4198 or RL7 and get a faster almost complete burn
but at about an 82% case fill which I am not thrilled about.

With that I am somewhat concerned about hangfires and or secondary ignition etc.

I could also load a fast powder and use a filler which I am not too wild about.

So I call Hodgdon, they would not even discuss it.
Great.

I called Barnes and they said just load it up with H4895. 80% burn.
At least they talked to me.

Another option I ran into is supposedly you can shoot a 458x2 american wildcat through a 458 winmag chamber.
458x2 American is a winmag case shortened from 2.5" to 2".

So lop off 1/2" from the winmag case, trim it and load it as a 458x2 American.
Basically the same as a 450 marlin but with the normal WM band, and about the
same ballistics as a 450 marlin or a hot 45/70 load.

If I load the 458x2 up with a 300 gr bullet and RL7 or 4198 a 104% case fill gets me to the
exact speed I am looking for at about 40-45k with about 4-5# less recoil due to less powder.

The 458x2 would actually run through a Short action which would be nice for a light rifle
although from scratch a 450 marlin would make more sense.

Sort of the same thing I do with my 44 magnum handgun, which is load light loads in 44 special which is safer.