An old Dude's recollection:
In the 70's, when +P ammo was a relatively new phenomenon, the question OFTEN arose as to what guns were safe with +P.
S&W put the word out at that time that "ANY S&W with a model number stamped in the frame WOULD BE SAFE with +P ammo".
IF anyone cares to search the "Reader's Questions" sections of magazines like "Shooting Times", "American Rifleman", and "Guns & Ammo", you will probably find that S&W quotation. Look in Skeeter's and Elmer's columns around 74-76 to start with, and the "Questions" in the "Amer Rifleman".
The "with a Model Number" statement would have precluded the ALUMINUM cylinder guns built in the early 50's.

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Regards,
Lee Jarrett