Believe it or not (I saw it with my own eyes), the only gun they ever had fail in 20 years was a Ruger GP100 with a blown forcing cone. Sure enough, a nice sized chunk (call it about 2 to 3 mm worth of material) was blown away from the 6 o'clock position of the forcing cone. All had been rented out equally over that time period. That busted GP may be the exception....
Yes, the variances can be due to the way the stainless steel is heat treated. Ruger has tight quality control, but every now and again a lemon squeaks through. I recall that two Kentucky cops complained that their holsters were wearing down the front sights of their Smith 681 revolvers. Closer examination revealed they were from the same batch and that there were other signs of extreme wear, including unusual wear and stress in the forcing cones. There were even some reports of stainless Ruger Security-Six forcing cones cracking, but strangely, only the stainless. Again, it was the rare exception and almost exclusively the earlier ones.
Still, any .357 can suffer the ill effects of shooting 125gr JHPs. A forcing cone doesn't have to crack. The edges can wear and angles change. The throats of the cylinder can also allow gases to blow past the bullet and wreak havok on the topstrap and the forcing cone. This is far more likely with Taurus revolvers than Smith and Ruger, both of whom have better quality control. The poor man's way to check the throats is to drop a new .357 jacketed bullet into each chamber and see if they fall through. I've seen many Taurus revolvers where the bullets just drop right on through. If that happens, you can bet that gases will escape, too.
Most Smith and Colt revolvers have 11-degree forcing cones. Ruger, I understand, uses either a 5-degree or 8-degree. I've been told that this offers a bit more protection. You may get a little more fouling with lead bullets from a 5-degree forcing cone, but it won't affect accuracy with jacketed bullets.
Colt never warrantied their revolvers against cracked forcing cones, and some of their Pythons suffered from them, and Smith says flat out not to use light bullets (under 158gr) in their K frames.
The bottom line is that I would use light bullets sparingly in all my revolvers. The one thing not to do is to have a barrel "fixed" or repaired. The hot gases cause leeching of the steel which causes fatigue that cannot be seen but which is, nevertheless, there. Turning back and re-reaming the barrel cannot fix that fatigue. Stainless steel also significantly resists that leeching, so that is one more reason to go with stainless.
Rugers still offer the greatest resistance, but there's no doubt that N-frames and even L-frame are far better than the K-frames. It makes me wonder why the K-frames are selling for as much as they are, but it undoubtedly has more to do with their cosmetic appeal and their wonderful craftsmanship.
The Security-Sixes will still drink them under the table, though.
