Jimmy,
I'm in pretty much agreement with most of what's been said here about the high pressure loadings, especially in the older K Frames and the .38 Special only J Frames. Split barrels can and have happened, as you very well know! Some of those were likely the result of the barrel having been overtightened a bit during inital installation and may? have split with any round fired at some point in time. Documented instances involved both low numbers fired as well as many numbers fired through the guns.
The early 125 grains in the magnum loads were certainly higher pressure rounds and the flame cutting was worse with them than compared to regular magnum rounds with heavier grain bullets. Lots of possibilities with no real specific correlation to anything much. But, when those hot 125 grain loads became available, a lot of folks fired quite a lot of them during the time the split barrel incidences became more frequent and more publicized. FWIW, I carried the same Model 19 4" for quite a few years. It had untold thousands of wadcutters and some thousands of .357 mag rounds through it during that time. I never had a problem and never personally saw a Model 19 experience a split frame or barrel. But that did happen. I watched my revolver closely for the problem. I have personally seen some of the alloy frames with split barrels and frames underneath the barrel, especially when higher pressure loadings than standard .38 Special were fired through them, plus know of some of those that were claimed to have only fired standard pressure loads. Who knows for sure? I have also fired a great many rounds through various steel J Frames and a few alloy frames, with no problems, starting about the time the first Super Vel loadings came on the market. Not a high percentage of those rounds were the higher pressure loadings, especially in the early airweight frames.
FWIW, the "cure" that we saw when the L frames were released was also applied to the J frames when they were introduced in the .357 mag chambering. The frame was strengthened and made stronger with the new size J frame. I've owned a Model 442 airweight since shortly after they were introduced. It's fired a good many +P .38 Specials as well as lots of standard pressure target loads. I bought my first good used Model 640-1 (Magnum J Frame) later and after the good Speer Gold Dots for short barrels were introduced. That revolver has had quite a few of the .38 +P rounds fired, as nearly as many of the .357 mag short barrel loadings have been fired. I generally carry and prefer the steel J frames about 90% of the time. And I normally carry the .38 +P loads because they fit any of my J Frames, I know how they shoot, where they hit, and I feel very comfortable that they are plenty good enough for what I want them do. Keeps things simple that way. The mag loads are indeed more powerful, but they are also noisier and a bit more of a chore to control. I feel that the .38 +P is sufficient!
I may have a cracked frame or barrel tomorrow, but I'm not worried about that at all. Based on my personal experience with rounds fired and having no incidence of problems with them in my revolvers, I will continue my practice. I haven't fired a 125 grain loading in any of my revolvers in a very long time. I like the heavier weight bullets and I tend to favor good penetration before great bullet expansion. Both of those things together is great, if you can get it, but expansion without adequate penetration is not acceptable to me. As I said earlier in this thread, my first five shots involve the full wadcutters loaded by Buffalo Bore, but I carry the Gold Dots because they are easier and more surely reloaded, especially under pressure, than the wadcutter shaped rounds. And it is my expectation and hope that after those first five (or less) are fired, a reload can be done without a great immediate necessity to reload and fire again to finish the job. Everything is a **** shoot and anything is possible, but I am comfortable with this level of personal protection and I am comfortable with these loadings being fired in my revolvers, both for adequate practice with them as well as performance in time of need. That's my opinion, FWIW.