I recently purchased a NEW M&P 340 and am experiencing a problem where after firing 15-20 rounds the cylinder when swung open does not rotate freely, it develops some excessive drag.
I removed the cylinder and discovered flakes of lead are accumulating in the yoke bore causing the binding. I scrape them off with my fingernail, lightly lube everything and GTG until the next 15-20 rounds.
What I did notice is my cylinder gap is all out of whack. Measured with a feeler gauge the driver side is .010 and the passenger side is .007. My gauge is too wide to pass through. This seems not only excessive but why the difference? Something bent? Not aligned correctly? I will call S&W tomorrow and see if there is anything they can do.