The AR bullet, 452423@ 240 grs with 7 grs Longshot.
I've also used the LBT 300 WFN with the same powder charge, but this is a custom bullet, not anything remotely commercial.
The Colt 1917 will also require a .454 diameter or larger bullet.
The Colt New Service in 45 caliber has more metal in the cylinder at the bolt notches and a larger bolt than any Smith 29 up to Endurance Package levels.
Everything I've ever shot out of a Colt 1917 is considered +P.
