Welcome to the forum
First, I would try a complete disassembly, cleaning, inspection and lubrication of the gun. There are so many issues, including dirt and old lubricants, that can cause the problem you reference here, that a shot at an actual diagnosis would be futile, pure speculation, and might even lead you in the wrong direction.
If you are unfamiliar with the disassembly procedure and what to look for, you can check with some of the local PD's to see if there is a S&W trained pistol armorer in your area, or a qualified/trusted gunsmith who is familiar with these models, who could have a look, and try to determine the problem.
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Ret. LE, FA Instr, S&W Armorer
Last edited by armorer951; 09-14-2016 at 01:51 PM.
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