Does anyone know when S&W started heat treating various frame sizes and what type of steel they were using at various times. Looking mostly from 1940 forward. Thanks

Most carbon steel guns now are made of 4140. Don't know any more specifics on this one.

That would be a question for Supica and Nahas (SCSW) or a super serious collector. I believe different models were heat treated and different times depending on the cartridges they fire. For example the Model 60 was heat treated specifically for +P ammo on the model 60-7 around 1993. Sorry I can not be of greater help on this one.

There have been reports that model stamped (post-1957) S & W revolvers were stronger than pre-model guns, which is why the factory used to state any steel model stamped K frame .38 Special was OK for the dreaded + P ammunition. Whether this was due to different heat treating, steel or other manufacturing processes is unclear. However, pre-war K frame .38s were advertised as safe with .38/44 loads (158 gr at 1100 fps). Not much clarity on this subject to me.

Historically, model 1917 Armys had then state-of-the-art heat treatment.

__________________
Alan
SWCA LM 2023, SWHF 220

Unfortunately, talking with someone who works (or worked) at S&W in some technical capacity is about the only way to answer such metallurgical questions - assuming he would talk. I am unaware that S&W gave more than casual mention about model-by-model details about steel alloys used and heat treating methods. It has been mentioned that different alloys and heat treatment methods were employed in the development of .357 and .44 Magnum revolvers. A competent metallurgist could probably perform testing to determine the alloys used and heat treatment performed if you gave him a gun to work with. But you wouldn't want the gun after he finished with it.