Home Forums Hunting & Shooting Express Rifles and Big Bores Only The great 458 Winchester. Everyone should own one at least once

I put out a request for IMR-4198 and AA-1680 loads with 250gr Monoflex and 258gr CEB in the .458 WM & .458 B&M at the B&M Forum.
Will see if I get a response.

Meanwhile, I will say that I tried AA-1680 with the 300gr Sierra ProHunter, a very soft bullet.
Results for that bullet with 69.0 grains to 76.0 grains were kind of wild.
76.0 grains got it over 2800 fps MV at which point the bullet vaporized in my muzzle brake and destroyed a chronograph.
One bullet before that actually made it to a 25-yard paper target as lead dust and read 2798 fps over the chrono before that last bullet.
Generally wild extreme spreads.
Best 3-shot load was 73.0 grains of AA-1680 giving 5-yard chrono readings like this: 2715, 2715, 2726 for ES 11 fps, st.dev. 6 fps.
It might be a better powder for the lighter 250-258-gr bullets.
I never worked with it again,
but it might deserve a trial with 250-ish grainers.
I would start with 66 grains and work up to 73 grains.
Also, a standard large rifle primer might be tried instead of the F-215 magnum primer I used.

See mid page 104 of this thread for my preferred 250-gr Monoflex loads with H4198 and AA-5744.
Those would probably work well with 258-gr CEB.