I've been exchanging emails with C.E. "Ed" Harris, who many will remember from his days as the head of Q.C. at Ruger - when they experienced a similar problem. Here's what he had to say: ----------
"Old problem rearing its ugly head again, not really a new problem. A troublesome sporadic one when people forget about good shop practices and get sloppy.
Stress corrosion cracking is generally caused by contamination by solvents or cutting fluids too high in chlorides. Over-torquing barrels barrels creates a stress rise at the root of the thread which makes the problem worse. Microscopic examination of the failed barrels would be obvious to a competent
engineer, especially familiar to those with aerospace or nuclear power systems experience.
Ruger had a short run of this back in the 1980s when they first starting making stainless magnums. I saw a few dozen guns come back when I worked there. All were traced to one guy on night shift who was over-torquing barrels on Redhawks which didn't quite line up, instead of taking a pass off the front of the frame on a Blanchard grinder as he should have done. He also used a wrong, slippery high sulphur thread lubricant intended for chrome-moly instead of the anti-seize compound used with SS.
This condition is aggravated by tight fit of barrel threads, such as when using a class 3A, combined with high stress, high temperature, and high barrel torque. Ruger fixed their problem by changing to a looser 2A fit on the barrel threads and assembling barrels to the frames using a Loctite product to cement them solidly while reducing stress on the threads and positively preventing any seepage of cleaning solvents into the barrel threads after they left the factory."
This wouldn't be the first time S&W has contended with the problem; the Model 442 Airweight Centennials, particularly in nickel finish, are somewhat notorious for frame cracks under the barrel. A phone conversation with a S&W representative confirmed to me that those problems were caused by over-torqued barrels.
However, there's always the possibility of user error, such as the use of certain products that contain chlorine compounds (brand name removed for obvious reasons):
"Use of [lubricants containing chlorine compounds] "could" do it, as could any number of other cleaners, especially if used with an ultrasonic which enhances thread penetration."
There are certain "miracle" gun lubricant products out there that contain chlorine compounds, and have become popular amongst the more "martial" crowd. In addition, ultrasonic cleaners have been very popular at many police agencies over the last decade or so, and it wouldn't surprise me to find either (or both) in use at the affected department.
Given Ed's expertise, I suspect that his analysis is pretty close.
-=[ Grant ]=-