Howdy Again
Regarding the strength of an old revolver when it was manufactured vs how strong it is today, I would say the only factor would be corrosion.
If a revolver, particularly one from the Black Powder era, was cleaned properly back then, then there should be no corrosion and the gun should be just as strong as it was when it left the factory.
However if it was not properly maintained, and there is corrosion present, all bets are off.
I have lots of old guns from the Black Powder era. Old Winchesters, a Marlin, quite a few Smith and Wessons, and three Merwin Hulberts.
It has been my experience that finding bright shiny bores and chambers in a firearm from the Black Powder era is a fairly rare experience. Not unheard of, but most of my Black Powder era guns have pitted bores and chambers. This is an indication that they were not always well cared for. So as a rule, I never shoot any of these guns with anything but Black Powder. Yes, it is possible to reproduce Black Powder pressures
and pressure curves with Smokeless powder, but generally speaking these are not powders that are generally used in revolvers. So I don't go there, I only shoot my old revolvers with real Black Powder. Rifles not so much. The breach and locking mechanism of most rifles is usually much stronger and thicker than with a revolver. So many old rifles from the BP era, even though they exhibit a pitted bore, are reasonably safe to shoot with light Smokeless loads, as long as the mechanism is in good working condition. Revolvers are a different story. The weakest part of most revolvers is the thin section of metal between the chambers and the cylinder locking slots. If a revolver is going to let go, that is where the failure usually starts.
That is what happened to this old Merwin Hulbert.
The cylinder first let go at the locking notch, then the crack propagated along the thinnest sections of the chambers. One piece lifted off and took the top strap with it. Notce how the two neighboring chambers almost let go too.
I own this Merwin now with a custom new cylinder and a custom new top strap.
This 44-40 Open Top Merwin I would not dream of firing with Smokeless powder. Only Black Powder.
The same with a couple of Smith and Wesson New Model Number Threes, a couple of Schofields, and a Russian model. Plus a whole bunch of S&W Pocket Pistols. I would not dream of shooting any of them with anything but Black Powder because they were designed and built during the Black Powder era.
Colts are a little bit different, Colt started marking their revolver with a VP in an upside down triangle for Verified Proof shortly after 1900. This meant the steel was strong enough for Smokeless powder loads.
I have a couple of 1st Gen Bisleys from 1907 and 1909 that I could probably safely shoot with Smokeless loads, I just choose not to.
So again, I will not shoot any revolver that was designed and manufactured during the Black Powder era with Smokeless powder. If it is not in good condition I won't even shoot it with Black Powder. In fact, unless it is a collectable, I won't even buy it at all.
Yes, I do have a few collectable BP era guns that I do not intend to shoot at all, even with Black Powder. Like these S&W Tip Ups. I bought them because I am a S&W collector, and they have fascinating mechanisms. But since Black Powder 22 Rimfire shorts are not available anymore, they will not get shot by me.
This #2 OId Army was converted from 32 Rimfire to 22 Rimfire by sleeving the barrel and chambers. I felt the sleeves were probably strong enough to take the pressure of Smokeless ammo, so I have fired it with low powered 22 Longs from CCI. But it is an old gun, everything dates from 1862, and I don't want to overdo it by shooting it too much.
So, why should an old revolver not be as strong as when it was made?
My answer would be corrosion. In a revolver, if I see a lot of corrosion, I am not going to shoot it with modern Smokeless loads.
As for the Iver Johnsons, the BP models were perfectly safe with Black Powder when they were made. They were not safe to shoot with Smokeless. That is why IJ changed the steel at the turn of the Century. I would not shoot one of the BP era ones with Smokeless today or 100 years ago.
By the way, regarding pitted barrels, it has been my experience that with a pitted barrel, reasonable accuracy can be expected out of any old revolver or rifle, as long as the rifling grooves are still strong.
P.S. Not revolvers, but much has been noted about shooting old Damascus barreled shotguns today. Again it is a matter of time and corrosion. There are many, many feet of welded iron and steel in a Damascus barreled shotgun. While it was probably proofed at the factory, and was perfectly safe to shoot when new, there is no reliable way to know if hidden corrosion has attacked the welds over time, and whether the gun is still safe to shoot.
Corrosion and time.