I had a fun thing happen - bought a 1914 Colt 'New Service' in .455 which the Seller said had been converted to .45 ACP and Moon Clips.

Nice old Gun, so I figured what-the-heck.

I get home, and, I find that .45 ACP and Moon Clips will not permit the Cylinder to Close.

I try .45 ACP CArtridges by themselves, and, they fit well, the Cylinder Closes well, and, I suppose they would fire fine, as their Head Space appears to be about right...but, one would have to eject them with a Pencil or something.

.45 Colt is too long.

A little time goes by, and, I am at a Gun Show and a guy has a Box of .455 Cartridges and I buy them...I get home, and, "Bingo", they fit perfectly, and, the Cylinder closes perfectly, but appearently, the old Colt Cylinder was shaved just a little, and, it does allow .45 ACP to fit with no Moon Clips, ( whether the shaving had anything to do with it or not, I do not know ) so, there is yet one more variation on the theme.

If I put a .45 ACP Cartridge into the Muzzle, so the Bullet itself is in the Bore, it goes in all they way to the Cartridge Case mouth, so, this suggests to me that again, as usual, a .45 ACP Bullet is way too small for a .455 Barrel.