What Archie says!
You can't go wrong with anything in his well-worded post.
Smith & Wesson adopted numeric model designations in 1957, stamping the model numbers on the inside of the front of the frames, viewable with cylinder opened.
Now Archie's advise is sound and most worthwhile but being a bit of a nitwit whose shooting career began about the same time as +P ammunition hit the market, I've fired any of several pre-1957 Smith & Wesson K-Frame .38 Special revolvers with all manner of +P ammunition and some similarly healthy handloads. Got clean away with it too though it cannot be recommended to others. Perhaps the goodness of Smith & Wesson saved me from myself.
Back in early marriage my wife's bedside gun was a S-series K-Frame 5-inch Smith & Wesson Military & Police revolver made in the 1946-1948 time period just exactly as bill35738 describes. It occasionally was fired with an assortment of heavy loadings including the so-called "FBI load" which is the +P load with 158 lead SWC bullet, similar handloads stoked with 158 grain SWC lead bullets and 5.4 grains of Unique, and even some Winchester Western +P+ 110 grain JHP "Treasury loads" when a friend of my parents who actually worked for the U. S. Department of the Treasury gave me an occasional box. No ill effects were observed.
+P 158 grain loads have also been fired in a Smith & Wesson Victory Model from 1943 kept around here as well as the revolver seen in my avatar which was produced in 1926. They both eagerly ate up the ammo.
Over the years I've also shot 158 grain factory +P loadings through a succession of Colt .38 Special revolvers dating back to 1913 with no ill effects observed.
I've related the story on the Forum in the past of a lawman friend of mine who, early in his career, was given a K-Frame Smith & Wesson Victory Model revolver by a respected mentor. He carried this gun for many years. By the time I met him he was working for an agency which issued the Winchester .38 Special +P 110 grain JHP loading. He could get all this stuff he wanted for practice, liked to shoot, so poured quite a lot of it through his World War II vintage revolver. The first time I went shooting with him I was scrounging all his brass which he didn't want. Each and every empty case had a distinct step about half way up its side. Puzzled, I asked to examine his revolver closely and found a similar step cut midway in his cylinder's chambers. I also found that the caliber designation on the right side of the barrel indicated ".38 S&W CTG." What he had was a Victory Model supplied to the British. These were chambered for their military issue .38/200 round which we know as .38 S&W here in the U.S.. The revolver was one which had been surplused, had its chambers reamed to accept the .38 Special, and sold, probably back in the 1950s-1960s. Lee Harvey Oswald used one of these to murder Dallas Patrolman J.D. Tippets during the event of the JFK assassination.
Sam had been hammering his revolver for several years with this load having the +P designation. I expressed some reservations about the expediency of subjecting the revolver to such treatment but Sam just shrugged as he reloaded six more rounds and said if it was going to let go it would have done it by now. The revolver gave every indication of being perfectly sound.
Smith & Wesson is said to have introduced improved heat treatment processes for their K-Frame revolvers in 1919, beginning with revolver serial number 316648. The Jinks and Neal book "Smith and Wesson: 1857-1945" also refers to some sort of early effort to harden cylinders beginning in 1909. It must be remembered that when the .38 Special cartridge was introduced in 1899 (and not in 1902 as so many reference works suggest) it was a black powder cartridge, using 21.5 grains of the stuff with the standard 158 grain round nose lead bullet. Several good smokeless propellent developments were already on the market and almost immediately the ammunition manufacturers began supplying .38 Special cartridges loaded with smokeless powder which offered different pressure curves and performance characteristics than black powder. Throughout the 1890-1920 period especially, firearms manufacturers developed improved materials to better handle the new propellents. Now "hard" steel doesn't necessarily equal stronger steel. What is desired in the heat treatment process is to produce "tough" steel.
I've long held the notion that the .38 Special "+P" designation is a "tempest in a teapot" and such ammunition isn't nearly as fearsome as it's internet forum reputation suggests. Stop and think about it. In today's litigious society it is inconceivable that a manufacturer would actually release an ammunition product for a
very common and standard handgun that
really could cause catastrophic failure if used in some of them, dire warnings aside.
SAAMI has fiddled with standard .38 Special pressures over the years, redefining it. Definitions of standard and +P .38 Special pressures have been a moving target in the past.
Having this scroungy looking but mechanically sound old Smith & Wesson Military & Police K-Frame revolver on hand, not being a family heirloom and acquired with little cash outlay, it was determined to run some +P ammunition through it as an experiment during a chronographing session conducted a little over a year ago. This revolver was produced in 1904 only 5 years after the model's 1899 introduction and 53 years before Smith & Wesson's arbitrary 1957 cut-off prohibition on use of +P .38 Special ammunition.
A total of 30 rounds of different factory 158 grain +P loadings were fired through it in three different 10-round batches. The old wheezer revolver performed like a show pony. Nothing became unhinged and the empties just fell out with a bump of the ejector rod.
It could have grenaded on the 31st round but bet it wouldn't. I did make the decision to avoid shooting some Buffalo Bore +P ammunition through the old revolver as their ammunition gives every impression of being a truly heavy loading.
If emergency circumstances required it's use with +P ammunition I'd feel grateful to have the old revolver in my hand and concerns over it's performance wouldn't intrude. As it is, there are other .38 Special revolvers on hand for serious social purposes. This one mostly serves as a reference of the characteristics of the early Smith & Wesson Military & Police revolver, one of a host of K-Frame revolvers built for over 113 years as of this year.
Bottom line: While I won't unnecessarily subject my older .38 Special revolvers to use with +P ammunition I ain't worryin' about +P as being dangerous to either gun or shooter. This is only personal opinion and should be taken with a large grain of salt.