I have 3, 40fs doesn't stay down, my 9c and 45fs stay down. The 40fs was my first M&P, it stayed down the first few times, but then one day I messed up a little while installing the slide and jammed it up a little.Once I figured it out, it wouldn't stay down anymore.. no big deal... it comes apart when I clean it, goes back together when I'm done...

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Jack C