Howdy
Oh boy, one of my favorite subjects.
Here is part of the instructions that came with one of my R&D cylinders for my Remington 1858 Cap & Ball revolver.
Notice at the top right it states "45 Long Colt "Cowboy Ammunition.............loaded to 750 fps to 850 fps is what they recommend.
OK, here is the first fallacy with that statement. Velocity is not the controlling factor that determines what is safe to fire in any firearm and what is not safe. PRESSURE is what determines what is safe and what is not safe. Using different weight bullets and powders with different burning rates it would be easy to construct ammunition that did not exceed 850 fps, but could vary widely in the pressure it generated. One person's 850 fps reload might be perfectly fine in a particular cylinder, somebody else's 850 fps reload might blow up the cylinder. So the velocity caution is meaningless.
Second fallacy: there is no nationally recognized standard for 'Cowboy Ammunition'. Cowboy ammo is what ever the manufacturer decides, and labels as such. Search SAAMI and you will find no reference to Cowboy Ammunition. You won't find any reference to 45 Long Colt either, but that is a discussion for another day.
As has already been stated several times, the cylinder of a revolver is the pressure vessel, not the frame and not the barrel. If a revolver lets go, most of the time it is the cylinder that bursts.
Like this.
I have no proof of this but I strongly suspect most Cap & Ball revolvers are made of relatively soft steel that has not been heat treated to strengthen it. That only makes sense, seeing how cheap Cap & Ball revolvers are, compared to cartridge revolvers.
Now look at what type of steel was used in my cylinders. 4140 for the cylinder and 4150 for the cap.
A quick google search of 4140 steel came up with this:"AISI
4140 steel grade is a versatile
steel grade. It is a chromium-molybdenum alloy
steel.
The chromium content provides good hardness penetration, and the molybdenum content ensures uniform hardness and high strength. ASTM
4140
chrome-molybdenum
steel can be oil hardened to a relatively high level of hardness."
Revolver manufacturers have been routinely hardening their cylinder since the 1920s. I would be very surprised if my R&D cylinders were not hardened for Smokeless pressures.
He asked what material Whitacre used, and I looked it up, and metallurgically, the stuff was not better than the material used in plumbing pipes, it was very low grade. The material was barely a steel, it was a low, low, carbon steel, just above wrought iron. But, it cut easy and was perfectly adequate for blackpowder. I can't find that email anymore, but it was interesting!
You may find it interesting to note that early Colt Single Action Army revolvers had cylinders and frames made of iron, not steel.
Here are some notes I copied from Jerry Kuhnhausen's The Colt Single Action Revolvers a Shop Manual:
"1st Generation S.A.A. cylinder material changes began to occur at about the same time that S.A.A. frames were being metallurgically updated. Cylinders prior to approx. s/n 96,000 (mid 1883) were made from materials generally resembling high grade malleable iron. Original cylinders from approx. s/n 96,000 to about 180,000 (mid 1898) were made from transitional low/medium grade carbon type steels. These cylinders and their parent frames were not factory guaranteed for smokeless powder cartridges. Cylinders after frame s/n 180,000 (mid 1898) began to be made from medium carbon type steels. Later versions of these cylinders were better and more uniformly heat treated. S.A.A. revolvers with cylinders of this final type were factory guaranteed in 1900 for standard factory load smokeless powder cartridges."
Incidentally that includes the frame. I have no idea why I have not read accounts of users of smokeless cylinders reporting damage to their black powder frames. I consider the entire practice of using smokeless rounds in black powder frames dangerous.
The manufacturers of conversion cylinders for Cap & Ball revolvers specifically state their cylinders should only be used with steel framed C&B revolvers. Not brass frames. Perhaps you have not read of any cases of damage to Black Powder frames caused by shooting Smokeless rounds in conversion cylinders because there have not been any. Nobody is saying to shoot high velocity or Plus P type rounds in these revolvers. The pounding of recoil probably would cause stretching of the top straps if nothing else. Personally, I am not crazy about the idea of shooting Smokeless cartridges in open top Colt type replicas. I have a couple of original Colt and Merwin Hulbert open top type revolvers, and the barrel gaps have definitely opened up over the years because over time something has stretched. But my top strap style Remington 1858s with their cartridge conversion cylinders have not seen any damage.