FEI, +P ammo is just another industry money-grab taking advantage of consumers, most of whom don't have a way to velocity check ammo, certainly no way to pressure test ammo, and no awareness that modern powders can deliver +P equal results with lower chamber pressures than standard pressure loads using different powders! On top of which, an added 2,000 psi is a far cry from anything close to frame busting, cylinder-exploding pressure! The industry standard for "proofing" modern revolvers is around 40-50% over standard pressure. If we use the SAAMI standard 17,000 "average psi" that means ALL .38 special revolvers (certainly those from reputable makers) are engineered to handle 23,800 - 25,500 "average psi". Even if one added a rigidly defined "2,000 psi" to the baseline, +P ammo would only rise to 19,000 psi which is still well below the maximum AVERAGE pressure the gun is built to survive. Any gun that is sensitive to being "blown up" with a piddly 2,000 psi increase in average pressure should not be on the market - and isn't.
No matter if S&W or anyone else publicly rates a .38 for +P, they should ALL stand up to it without a problem, and without ANY doubt, if an alloy J-frame can handle +P loads, so too can ANY steel frame, and more specifically, it's the CYLINDER that's got to contain the the pressure and they're all heat treated to meet the same standard. As for frame damage or even reduced life of a steel J-frame due to breech face thrust, the difference between standard and +P is insignificant, especially in all bullet weights below 158 grains.
The +P scam is no different than the JHP cash grab. For decades, the .38 special was known as a reliable "man-stopper" using plain old 158-200 grain lead - usually swaged ROUND NOSE lead bullets, with SWC noses being preferred when available. Of course swaged lead slugs are ideal for sub-magnum loads, crimp on a gas check and they work pretty well in some magnum loads! Swaged lead slugs are fairly soft - not unlike the old pure lead balls of C&B yore and readily deform upon impact and as they plow through muscle, fat, and bone. All one need do is revisit the video clip of Oswald being popped by Jack Ruby to know a .38 special to the abdomen ain't no joke! Even today, many experienced shooters choose to carry 158 grain lead SWC in their J-frame - when they find it, or load their own, over all these expensive, ultra-light, reduced recoil "+P" loads that don't even come CLOSE to the chamber and breech pressure exerted by a standard .38 LRN!
This reminds me of the industry deliberately downloading 9mm ostensibly because of the all the foreign made pistols "flooding the market" after WW2 by as much much as 100 fps on average, then, years later, along comes - you guess it, +P ammo loaded back closer to European mil-spec, but still decidedly less potent that military loads. The excerpt below is taken from an April 23rd, 2019 American Rifleman article:
"In our tests in 1985, XM882 propelled a 124-gr. round-nose FMJ out of the 5" barrel of an M9 at an average of 1273 f.p.s., delivering 446 ft.-lbs. of energy at 15 ft. Using an Oehler Model 43 and firing the new ammunition out of a 4.7"-barreled P320-M17, M1152 with the 115-gr. bullet was at 1326 f.p.s. and 449 ft.-lbs. of energy, while the M1153 (147 gr.) clocked 962 f.p.s. with 302 ft.-lbs., both at 15 ft."
THIS is the ammo every 9mm handgun is "built to handle" yet 95% of OTC commerical 9mm ammo barely breaks 330 ft-lbs. of energy. No wonder the 9mm is disdained as being "weak" and ineffective. The difference between an impact speed of 1,150 fps versus 1,326 fps is far more relevant to terminal effectiveness than iffy hollow point expansion versus a flat nose FMJ carrying a supersonic shockwave into the wound.