I've never had a .458 Win. Mag. but did have a couple. 458 2" "Americans," as well as a wildcat I sort of made up using a de-rimmed. 450 Alaskan case with a related rim to .532" to fit a standard magnum bolt face. I cut the new extractor groove at the same time.
This case, in a Model 70 (unfortunately post 64), had a capacity 7gr. greater than the .458 Winney Mangulum. It easily made 2,200fps with 500gr. Hornady's. I did not enjoy shooting those so I loaded it to the 2,150fps. with the 400gr. Barnes Spitzers(old style) I did enjoy shooting. The trouble was it took almost 10gr. MORE powder than the .458 2" to get that vel. So, I cut her back, rethreaded and chambered it for my .458 2" with the 3/8"leade. That allowed a normal seating depth as if the case was 2.2" in length. It easily did the 2,150fps with the 400's, 2,296fps with 360 Horn RNs and 2,059fps with the 500gr. Hornady RNS. I didn't shoot many of those, preferring the lighter bullets.

Incidentally, the difference between the Lott and Watts chambers happened on purpose and was at the end of the chamber's mouth.
Bench rest shooters call it the mean little shoulder. That is the 90 degree angle at the end of the chamber where the end of the case is supposed to just clear by .005" or so. It is then cut 45 degrees up to bullet diameter for the leade, but that mean little shoulder still exists.
What that shoulder did in the Watts chamber when fired with .458 Win Mag ammo, is strip off guilding metal from the side of the jacketed bullet when it road over that, into the throat(leade). This would prevent later chambering full length Watts ammo until the guilding metal was removed. This usually required a chambering reamer.
The "original" Lott chamber has a 3 degree angle from the case mouth of the chamber to the leade/throat. The bullet easily road up that slope into the leade and prevented the stripping of jacket material, if the shorter ammo was chambered and fired. This info from Jack himself, in one of the gun magazines when explaining why his chamber over the original Watts chamber. Small changes can make a difference.