Matt - I don’t believe it is necessary to shave the back of the cylinder of a 1917 Colt or Smith and Wesson revolver to make it a .45 Colt-caliber. I forget off hand if this conversion works well with the Smith and Wesson. The headspace is such on the original cylinder so as to provide a gap necessary for the head of the cartridge and the clips in which they were loaded for these revolvers. That gap, I believe, it relatively suitable for .45 colt. The shave cylinders were for the use of .45 Auto Rim ammunition without clips. That was a more normal conversion for these, which leads me to believe that there might have been features of the .45 Colt cartridge that were problamatical for these cylinders. I am not sure of that - all I know is that the gunsmith to which we contracted much preferred the .45 Auto Rim conversion.
Regarding the above mention of shaving of cylinder backs, I forgot in this original posting (this is a “edit”) that this alteration was done not to actual US Model 1917 Revolvers in .45 ACP, but rather to the ones sent originally to England in WWI, both Colt and Smith and Wesson, in .455 Webley California. There would be no reason to alter any Colt or Smith and Wesson Model 1917 in .45 Auto Caliber, nor any Colt New Service Model in .45 Colt, since ammo has been plentiful in both calibers since their inception. Hundreds of these revolvers in .455 were altered due to the scarcity of .455 ammunition. The same was true of Webleys, that were altered to take the .45 ACP in clips or the .45 Auto Rim, which didn’t need or use clips.
You wouldn’t shave the back of a .45 Auto-caliber Model 1917, because the headspace already allowed for the half-moon clip - quite a large gap. No purpose would be served. I can’t think of any way, aside from the fact that such a conversion would be relatively senseless, that you could convert the .45 auto-caliber revolvers to .45 Colt at all. As I recall the .455 Versions converted quite easily to .45 Auto Rim and or clip-loaded .45 ACP. The .455 Colts converted well to .45 Colt but I seem to recall that the cylinders of the .455 Sjmith and Wessons were slight shorter, and would require special bullet seating by handloaders if converted to .45 Colt. If I am correct, .45 Colt factory loads had the bullets prljecting past the face of the cylinder, an impossible situation.
As far as in its original form with the .45 ACP cartridge with those glass bullets,
It should be remembered that these revolvers were, for the most part, not bored straight through, but rather properly chambered for the .45 ACP cartridge. As such, the cartridge headstpaces on the case mouth. All that is then required is sufficient remaining length to accomodate the longer glass projectile, and I agree with DK that it appears to be of a length that would not protrude from the face of the cylinder, blocking its revolving action by hitting the rear of the barrel.