Rechambering Model 70 Safari Express in .458 Win Mag to .458 Lott

[Riflecrank]

Take a gander at how the exactly same powder charge in a .495 A-square beats a .500 Jeffery with exactly same barrel (26", 1:10" twist) and bullet weight, 570-gr:

.495 A-Square: 104 gr of H4895 >>> 2406 fps, sub-Pmax and most uniform of all for pressure SD/ES

.500 Jeffery: 104 gr of H4895 >>> 2348 fps, exceeds Pmax and wildly non-uniform for pressure SD/ES

 

[colorado]

That's just because you're running the 500 jeffery at the original 1920 pressure levels. With a strong action and new brass you can easily attain 2500 fps with a 570g bullet with the 500 Jeffery.

 

[Riflecrank]

Yeah, right.
Still shows that the li'l .495 A-Square can beat the "classical" .500 Jeffery jumbo-killin' ballistics,
and does it with less recoil for whatever ballistics if same MV with same bullet as the .500 Jeffery.

Yes, comparison point here is the 3300 bar MAP for the .500 Jeffery versus 4400 bar MAP for the
.495 A-Square.
And those are modern pressure standards of CIP, not 1927 vintage.

Higher pressure does the trick, and that may be a key to the uniformity and efficiency of the .495 A-Square.

Wait until that .495 A-Square gets a .458 WIN MAGIC throat and becomes the ".510 WIN MAG."
That will add another 100 fps to MV at same 4400 bar MAP.
Slicker feeding than a .500 Jeffery.
And the .510 WIN MAG reamer would be perfect for re-throating the no-throat, short-necked, rebated-rim .500 Jeffery.

 

[Riflecrank]

That will work in an M70 Winchester with 3.6" magazine box but that will cramp the nose room just like in a .458 Lott, tisk, tisk.
If you scale up a .458 WIN MAG to .510 caliber, that 3.340" COL becomes 3.720" and really ought to go into a 3.8" magazine box.
Best use for a .458 WIN MAG M70 Winchester rifle
is to leave it as is, .458 WIN MAG.