We've seen in current threads that S&W began using heat-treated cylinders on .38 Special M&P guns in Sept., 1919.
I get the impression that some feel this makes guns made after that date to be safe with Plus P ammo.
I'm sure they are safer from a blowup or a cracked cylinder, but frames and yokes were not changed metallurgically , were they?
If not, frequent use of hot ammo is going to cause cylinder endshake sooner than with later guns, made of improved steels and current heat treatment .
Keep in mind that some hot ammo is hotter than the rest . Buffalo Bore is surely loaded to higher pressures than most.
This is why I sometimes caution against Plus P in old .38's, despite what some have said about blowups not happening in their vintage revolvers.
Just a thought...