[mrerick]

The actual difference between a standard velocity round and +P rated round is literally a few tenths of a grain of powder and generally the bullet profile. Perhaps a few hundred FPS faster.

I don't generally shoot them, and would only use them in self defense loads. They will stress your gun more than standard velocity.

For a fractional cent worth of powder, they charge 2x or more per round. Good marketing, especially during a shortage.

 

[mrerick]

As mentioned earlier, the original .38 special round had the power level of today's +P, and so was proofed to shoot the higher pressure round. In general (with some specific exceptions in lightweight guns with alloy cylinders) that applies through today's guns.

The lack of marked label of approval is more a legal issue than a physical or metallurgy one. Shoot an older gun with +P and don't expect anyone to come forward to guarantee the gun, or take responsibility for safety of doing it. The standard line would be, if you don't know for sure - don't do it.

There were specific points in time (I think in the 1917-1919 era) where heat treatment metal hardening processes were used to improve the metallurgy and resistance to higher pressure.

When did heat treated (hardened) cylinders start?

After looking around for the answer in other threads (and not finding it), I decided to just ask a question that has already been answered. Sorry... There has been mention of being cautious shooting modern ammunition through older S&W revolvers due to lack of cylinder hardening in earlier guns...

www.smithandwessonforums.com

I have a very early second change M&P, and in spite of it's likely ability to run +P, I'll never intentionally shoot the higher pressure rounds in it. It is well over 100 years old, after all...