Speaking of devices, and what might make them not work,

a story about once working on a S&W revolver.

I like their revolvers, they tend to be accurate and reliable.  This one was a target revolver that had an overtravel stop: this is a small piece held in and adjusted by a screw fits in a slot cut in the rear of the trigger guard, you can move it out so that the trigger can move just enough to drop the hammer.  Yeah, it's a target -shooting thing.

I disassembled it enough to reach and adjust the piece, then put those pieces back in, then put the sideplate back in, put in the cylinder, and tried it.  The cylinder stop wasn't working right, and after you pulled the trigger the hammer had to be pulled back slightly for the trigger to engage the sear.  Which left me sitting there wondering what the hell...

Take it back down, check everything(no, I hadn't forgotten anything), and finally thought "What did I change?", then took it back down and looked.  As that piece had rotated in the slot some of it now protruded from the back of that slot, so slightly that you almost had to feel it.  Loosen the screw, move the stop around, make sure none was sticking out on the inside, then put it back together and try it.  And all is well.  

That piece affected stuff far from it, and I'm not sure how.  Apparently it was affecting the trigger rebound slide enough- just- to cause this odd problem even though the slide fit back in.

Yes, I'd messed with such before.  No, this had never happened before.  And it won't again.