Those 1917 pistols are not made of heat treated/tempered steel
Yes, they are. Colt began heat treating the New Service cylinders in 1903. Smith and Wesson did not heat treat cylinders in that era, but the Army contract for the M1917 required heat treating.
Misleading advice and something you should know better, at least, I think this is something you should know better. I really don’t know your education level and whether you know anything about metallurgy, or are winging it. Regardless, showing how much you know about the history of these old revolvers does nothing to address the concerns of the original poster.
It is all and wonderful that Colt heat treated their cylinders, but something that you should have mentioned was that the barrels and frames of New Service revolvers are dead soft. Frame stretching, crane stretching, cylinder end shake, blown barrel throats are all to easy to do with the dead soft plain carbon steels of the era.
Memory loss is rather rapid for some people, but the metallurgy of the era was just awful. These 1917 pistols are almost 100 years old and the metal technology, process control technology was basically taste, touch, and eyeballs. The steels of these pistols are plain carbon steels which are weaker and have a much shorter fatigue life than the alloy steels in use today. Loads that a modern pistol will take will blow cylinders and frame straps in these old pistols. Also, the steels of the period have a lot of tramp elements because they did not have the means we have today to remove residuals. So the plain carbon steels of the era are going to be weaker than the same plain carbon steels used today. They will often have seams from inclusions which become a weak spot and stresses will concentrate blowing the cylinder or barrel.
And another thing, these pistols were never made to last 100 years, they were built under war time conditions which emphasized volume over all other considerations. Their rough finish shows the short cuts they were taking to get these things out the door, I have no doubt that marginal or substandard materials and processes were also accepted, just to get the things out the door.
It is impossible to determine the number of rounds one of these old pistols has already fired, from an internet post, but the fatigue life of these things is going to be less than a modern pistol, and in fact, based on the number of rounds through the pistol, the cylinder may be at the end of its lifetime now.
I have a 1937 ish S&W M1917 which I developed some 255 grain cast bullet loads. Because it is a prewar pistol, it needs large bullets (.454” or more) to avoid barrel leading. Elmer Keith recommended loads of 6.5 grains Unique in the 45 ACP and I found his loads to be excessively hot. I do not recommend any Keith load in any vintage pistol, the blast and recoil was excessive. I have put a 6.0 and 6.5 grain Unique load test for reference, but I would stay well away from them.
Because I shoot 45 AR loads in this M1917 and a converted MkVI Webley, I now use a load of 255 LSWC and 3.5 grains Bullseye. This is a very mild load, shoots well, and does not stretch the top strap of the Webley.
I prefer Auto Rim brass in this pistols, inserting cases on moon clips, and removing fired cases from moon clips, is a total bother.
Unless the OP has a pressure barrel to measure pressures, I would not assume that seating the bullet out will keep pressures to safe limits in these old revolvers. The slope of the pressure curve is exponential, not linear, and given the low margin of safety in these things, the risk of a blown cylinder is high. I would stay with low pressure loads in these WW1 era handguns. If the OP wants bear stopping loads, he ought to trade his vintage M1917 for a nice new 44 Mag, 454 Casull, or 500 S&W Magnum. If he wants hotter 45 ACP loads, he ought to trade his M1917 Colt for a nice new 45 ACP revolver. At least he can find a gunsmith and parts if he damages it.
This has not been discussed by anyone but, bust up one of these Colt Revolvers and you may not find someone who will work on them. Maybe someone here can recommend a good Colt gunsmith for the OP, because I sure don’t know anyone who will work on these old New Service revolvers. Neither the D, E, or I frame revolvers. And then there is the part issue for a 100 year old gun….
M1917 S&W Brazilian Export 5" Barrel
250 LRN (.454) 6.0 grs Unique thrown, R-P AR cases, CCI300 primers
20-Jan-02 T = 44°F
Ave Vel = 833
Std Dev = 25
ES 79.6
Low 789
High 869
N = 12
Heavy recoil, aimpt about 6" low at 25 yard. But very accurate
250 LRN (.454) 6.5 grs Unique thrown, R-P AR cases, CCI300 primers
20-Jan-02 T = 44°F
Ave Vel = 888
Std Dev = 31
ES= 103.3
Low= 844
High= 947
N=12
heavy recoil, aimpt 5 OC below target, too heavy a load
250 LRN (.454) 4.5 grs Bullseye thrown, R-P AR cases, CCI300 primers
20-Jan-02 T = 44°F
Ave Vel = 754
Std Dev = 10
ES = 39.5
Low= 744
High= 783
N=14
Mild recoil, aimpt 5 OC, accurate
250 Nosler JHP (.4515) 8.0 grs Blue Dot thrown, mixed cases, FED150 primers
20-Jan-02 T = 44°F
Ave Vel = 749
Std Dev = 24
ES =87.8
Low= 709
High= 797
N =12
Mild recoil aimpoint 5 O’Clock
