Ive got a used m&p 340 that ive had for almost a year. When shooting 158 grain 357 magnum ammo, 125 grain 357 magnum hornady critical defense and 357 magnum Remington golden sabre the cylinder is coming unlocked under the recoil. I am a left handed shooter and the guy that runs the lgs thought that my hand might be contacting the latch that unlocks the cylinder. I did some more testing firing slowly and watching my hand motion and that isn't the issue. Yesterday I had 2 cylinders of golden sabre and critical defense do It then I shot about 20 38 +p and 50 38 special monarch ammo through It and had zero Issues. I have successfully fired 357 Winchester pdx1, speer gold dot 38 special +p and hundreds of 38 special fmj target loads and hand loads and never had the issue happen. What could the problem be? Seems like
the excessive recoil is just loosening it up. The cylinder latch Is not loose you have to push on It pretty good to unlock the cylinder to load or unload It. I was going to just not worry about it since I normally carry 357 pdx1 ammo. Anyone ever heard of this? What should I do.

The cylinder locking bolt could be hanging up on a burr or shaving inside the frame..possibly keeping the ejector rod plunger from fully seating in the hole that is in the frame? Or the cylinder locking bolt spring is not compressing far enough inside the plunger, also causing the same situation with the ejector rod plunger/pin not fully seating in the frame. I also would check the ejector Rod Springs to make sure that the little plunger that sticks out of the ejector star has enough tension on it. It may be enough to just take the whole assembly apart and oil them and reassemble getting rid of any crud that might be in there. I think it's kind of a sensitive balance of spring pressures that hold the cylinder locking plunger into the frame under heavy recoil. It is fighting the spring from the cylinder locking Bolt, so even a little bit of crud under the cylinder locking Bolt could possibly be enough to keep the plunger from being fully engaged into the frame. Do you know if the revolver has ever been dropped possibly a bent crane? Probably the most painless solution would be to just send it back to Smith & Wesson... or you could just take it all apart and start looking at stuff if you feel comfortable taking the side plate off it's not really brain surgery you could probably go on YouTube and find out the proper order of taking things out and reassembling them. Another thought I just had if you look on the very front of your revolver underneath the barrel there is a little pin with the cylinder closed ..unloaded of course.. does this little pin stick out or is it where it's supposed to be as if the cylinder was open? You might be able to tell just by looking at the little pin if your cylinder is fully latched.

Stop shooting that gun. Cylinder coming unlatched while firing is *very* dangerous. There might be a lot of endshake, combined with frame stretching, causing too much headspace.

Either way, send it to the factory and tell them what's happening.

[QUOTE=American1776;139626571]Stop shooting that gun. Cylinder coming unlatched while firing is *very* dangerous. There might be a lot of endshake, combined with frame stretching, causing too much headspace.

Either way, send it to the factory and tell them what's happening.[/QUOTE

^^^^what he said. You say you purchased the gun used. Maybe this unlatching situation is the reason why the original owner got rid of it. Perhaps someone watched one of those YouTube videos and "bubba'd" the internals. In any case, do not fire it and get it back to S&W ASAP.

Kaaskop49
Shield #5103

I figured it out after comparing it to another almost new j frame that I own. The small ejector rod that runs through the cylinder was either too long or the tube that it runs through that threads Into the back of the cylinder was too short. It allowed the rod to go too close to the end of the tube and it wasn't letting the lock plunger seat far enough to keep it in under heavy recoil. I ground 1/32" off the end of it and now the plunger goes in further and now It keeps it locked. Ran 10 rounds of critical defense and 30 rounds of golden sabre magnum through it with no issues.