Adam500 said:What would cause my M&P to leave the last round in the mag and lock open? It did this 2 times in a row last time i was at the range. Both times with one round in the mag. This was using American eagle 9mm 115 FMJ.
IAShooter said:If RJP3579's response doesn't solve your issue, it could also be a weak slide lock spring.
Had the same issue with mine. Sent it to S&W and it was back in less than a week with a completely new slide lock and has worked flawlessly ever since.