One hint would have been to produce the M1917 revolvers in .45 Colt. They had to issue two kinds of pistol ammo, anyway (clipped for revolvers, unclipped for M1911s) so having two cartridges would have caused no added problems.
Since it was used in WW1 this might have been a good idea.
Maybe they could have used up their surplus Cavalry BP Schofield ammunition from the 1880s.
Howdy
The Smith and Wesson Model 1917 was chambered for 45ACP because it was a very convenient modification of the 44 Hand Ejector 2nd Model.
In 1914 S&W made the .455 Hand Ejector 1st Model, chambered for the British .455 Mark II cartridge. This was a retooled Triple Lock chambered for the British cartridge. The only modification needed was opening up the chambers and the bore for the .455 cartridge. 5,000 were shipped to Britain at the start of World War One. The British did not like the complicated 3rd latch of the Triple Lock, and were also concerned that mud could get into the recess in the barrel underlug, so a second version was made without the features of the Triple Lock, with just a simple under barrel latch. This model was produced from 1915 thorough 1917. Close to 70,000 of this model were manufactured, most being shipped to Britain and Canada.
I have one of these. Mine was shipped to Canada in 1916.
It bears the Canadian Broad Arrow acceptance mark.
At some point after WWI mine was modified with a new barrel and cylinder to fire the 44 Special cartridge, which was a common conversion of this model. Converting them to 45 Colt was also common.
The 1917 Model was a simple conversion from the original 44 (44 Special) Hand Ejector 2nd Model.
All that had to be done was open up the chambers and bore from 44 to 45, and shorten the rear of cylinder so the revolver could be fired with moon clips. The cylinder was shortened by about .035, but the chambers were given a 90 degree transition to the chamber throat so the revolver could be fired without clips, with the cartridges head spacing on the case mouth. Approximately 163,600 were made between September 1917 and January 1919. Approximately 25,000 were made for the Brazilian Contract starting in 1937.
45 Schofield ammunition was all loaded with Black Powder, and would probably not have worked out very well in the Model 1917. Besides, the larger rim diameter of the 45 Schofield ammunition would have meant modifying the ratchet teeth on the rear of the cylinder. Yes, I checked. the larger rims would not interfere with each other, but they would not clear the ratchet teeth.
The cylinder of the S&W Model 1917 is not long enough for 45 Colt ammunition. The cylinder on the one pictured above is 1.535 long. Current SAAMI spec for the 45 Colt cartridge shows a maximum length of 1.600. Allowing for a .060 thick rim, that means that 1.540 of the cartridge would need to be in the 1.535 long cylinder. I held up some of my round nosed flat point 45 Colt ammo with an Over All Length of 1.547 and allowing for the .060 thick rim, it would extend to within about .050 of the front of the cylinder.
45 Colt was a common after market conversion for the Triple Lock and the 44 HE 2nd Model, but it would not work in the Model 1917 with its shorter cylinder.