A friend had a 357 N-frame cylinder rechamber to 45 Colt. When he tested fired it a small hole blew through one of the cylinder walls into a locking bolt cutout.
And he wasn't the only one. I have read of cylinder stop cuts bulging or blowing out or even being cut through by the .45 reamer. One school of thought is that S&W took more care in cutting the notch of the .45 cylinders. Which flies in the face of the "all the same basic parts" theory. I have also read of S&W factory .45 Colt cylinders bulging into the stop notches with "Ruger loads."
This was the reason given by Skeeter Skelton for converting .357 Highway Patrolman and Blackhawk to .44 Special instead of .45 Colt, too thin chambers, especially under the notches.
On heat treatment, all I have to go by is a reprint 1939 Stoegers. The .357 Magnum is cataloged with cylinder of "Heat treated chrome-nickel steel." Thing is, the .38 Special M&P is said to have "chrome nickel heat treated cylinder" and the .32-20 version adds "heat treated chrome nickel steel cylinder of
extraordinary strength." Even the .32 and .38 S&W Regulation Police had "heat treated chrome nickel steel" cylinders.
Was the heat treatment different, as is commonly said? I don't know. Who does?
Sorry, I no longer have a connection with a metallurgist who could get a handle on it with a hardness check. Too bad, I would not mind a little dent on my M28 and M14, they are well worn and it would not show much.
Even thick steel, even "heat treated" is no substitute for sensible loading. Skeeter described testing his .44 chamber reamer on a M27 cylinder with a chamber "jugged" by overload. (He found that it would not hand ream smoothly and had to have a gunsmith set it up in a lathe.)
The brass isn't the same. The old .45 Colt cases (that Keith was using) were made by folding over the brass to form the rim of the case. The rim potion of the case was not solid/drawn brass. Hence, the term, "balloon head". They worked fine for shooting, once, but were not real good for reloading.
There are three types of .45 Colt (and other period) case, not two.
The original type described here is more usually known as "folded head." I think it dropped out of use before WW I and maybe before the turn of the century.
The "balloon head" which Elmer Keith was probably using was a drawn case with turned rim. The primer pocket can be seen protruding into the interior and the head and wall webs are thin; but the rim itself is solid. In fact, UMC headstamped this type of case "S.H." for Solid Head. They did not mean the present type of solid head in which the case head web is thicker than the depth of the primer pocket. Note that Elmer said "the case head blew off," not that the rim of a folded head case blew out.
Henry Stebbins wrote in 1960 of the unusual find of some "modern" type solid head .45 Colt empties on the range, "the only ones known to science", so the balloon head had a long, long run.
The biggest issue with balloonhead cases was not necessarily the design but that they were customarily loaded with corrosive powder/primers and if not cleaned quickly after firing, they were quickly weakened by corrosion.
I never heard of corrosive powder. Black powder will tarnish a case very ugly but the ones I left uncleaned for way too long did not display any pitting or loss of thickness. They finally cleaned up with ceramic tumbler media.
The potassium chloride residue of corrosive primers is not nearly as bad on brass as it is on steel. Lots of rifle reloading was done with chlorate primers and no failures blamed on it that I know.
On the other hand, ol Elmer may have run up on some mercuric primers. The army quit using them in 1898 but they stayed in commercial use for a while. In fact, some of the early "noncorrosive" primers were actually mercuric. That didn't hurt the gun barrel but it was death on the brass.
