Thumbcocker,
I understand & have read thru all of the posts, and perhaps one of the other suggestions will solve the issue, but I am going to add just a bit here to try to help out.
( Note - I am going on in this post with the Ruger revolvers like the SP101 &/or the LCR, which I am pretty sure use a firing pin & spring & not a hammer mounted firing pin, just so folks know which revolver I am talking about here.)
Also, I am not questioning your methods of reloading or cleaning, nor criticizing, just offering some things to consider if you have not already considered them.
Have you checked to see if the firing pin is freely moving in & out? IOW, perhaps there is some crud build up in the orifice the firing pin sits in & it is holding the firing pin from retracting all the way when the revolver is fired? Or, maybe even some issue with the spring inside, like being broken & a piece of spring "binding" the pin so it doesn't retract fully when the revolver is fired?
If the firing pin is not retracting all of the way back in as it should and/or is sticking out further than it should when firing it might puncture the primers. while it may just do it with those S&B primers, and not others, it may be something to check.
( BTW, I have not had any issues with S&B primers, but occasionally I have trouble with some of their brass.)
Also... Could you have put in just a bit too much powder by accident when working up the loads?
What I mean is, since I am sure you are loading up properly, but is it possible that your powder scale needs to be calibrated after being moved or bumped. Or, perhaps you had some issue with a powder throw from a powder measure that gave you some loads that were pushing the limit on pressure?
I have had powder scales, both beam & elect. that got bumped when I got up from the bench, and I had to re calibrate when I returned. ( I check calibration "every" time I start to reload, to prevent such issues, even if I just went to the head or to leave the bench even for a minute. I do so just in case I accidentally bump the scale & don't realize it, if it becomes "off". Just so I know it was calibrated & I don't throw light or heavy loads by mistake.
I do not use 231, but I have also had a powder measures that will "wander a bit( My old RCBS does it occasionally) throwing loads by the setting on the measure working loose a little & changing the weight increasing it a bit. ( I weigh each powder throw, so I can assure that I don't overload. Yes, I am a bit "anal" about it, but I don't recall having a single issue with over charging since I do it. )
There are also powders that will "bridge" & throw a lighter charge, then a heavier charge, or charges, as the "bridge" breaks apart.
While the things mentioned are possible, it does not mean that they all happened. It would just be some things I would consider, not knowing your methods or having the firearm to look at in my hands.
I would certainly also re-test those loads to see if it repeats with other S&B primers & then I would repeat with other makers primers as well to try to eliminate the primers being an issue. But I would be looking at the firing pin & spring first. It might just be some crud or something easy to clean out of that spot. Hopefully not a broken firing pin spring that is "trapping" the firing pin so it doesn't fully retract, or holds the pin out further than it should when firing.
I wish ya G'Luck! in solving the issue & if you do figure it out, Please return & let folks know what ya discovered so we all learn from this issue.