One of my cartridge inventories is what I call "Victory Brass". I take once fired .38 Spl, and lightly neck size, and then fire form in my converted Victory Chamber. When reloading, I turn the resizing die out 2 turns.
My Victory Specials all chamber fine and I haven't had a split case yet.
Backing off the sizing die slightly helps get decent case life with the .45 Colt as well. I size just enough to get the, to easily chamber.
The .45 Colt was designed in the black powder era where most pistol class cases had a tapered body and mild bottle neck.
The mild bottle neck on cartridges like the .38-40 and .44-40 helped seal the chamber fairly early in the ignition process to minimize gas coming back into the action on lever action rifles.
The tapered body helped rim ejector cartridges like the .38-40 and .44-40 eject more reliably as the entire surface of the case came out of contact very early in the ejection process.
The .45 Colt was intended for the rod ejector Colt SAA and as such they were not worried much about ejection. They did want maximum powder capacity however so they adopted a parallel wall case and no bottle neck, in order to get maximum capacity with as small a cylinder as possible for .45 caliber.
However, they covered their bets slightly by tapering the chamber .007" from mouth to base.