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

Data posted at MIB:



My comments:
This data compared to the standard (short-throated) .458 B&M with 20″ barrel makes perfect sense.
I lose a little more velocity than expected from the shortening of the barrel only.
Expected loss is 75 fps due to barrel shortening from 20″ to 16.875″.
From 20″ to 18″ = -45 fps, from 18″ to 16.875″ = -30 fps.
45 fps + 30 fps = 75 fps.
Maybe 5 fps is lost to faster twist,
and whatever else may be attributed to longer throat,
when comparing the standard .458 B&M loads fired in the .458 B&M+ Long Throat + Fast Twist.

The long throat allows making up for excess losses when we can add more powder safely.

If one should ever run a SAAMI .458 WinMag reamer into one of his .458 B&M rifles to re-throat it,
I SWAG he would find that AA-2230 gives higher velocity at lower pressure than H4198 does.
Free bore reduces pressure and creates the internal-ballistic effect of greater net case capacity,
not just imaginary.

Shortening from 24″ to 20″ also would produce only about 75 fps loss, with proper handloads.
Therefore, a 24″ barreled .458 B&M+ would be about 150 fps faster than my .458 B&M+ with 16.875″ barrel.
A 2350 fps load in the short barrel becomes a 2500 fps load in the 24″ barrel, with 400-grain bullets.
That is the result many of us get with our SAAMI .458 WM rifles with 24″ barrel, and non-SAAMI handloads.
Shucks, we might be over 60,000 psi by a little, and also might be a tad longer than 3.340″ COL with some loads.
No worse for the wear than with a SAAMI .458 Lott.