S&W M&Pc .40 range report: is there a premature slide lock fix?

[the naked prophet]

So my wife got a S&W M&P .40 compact, and in the first two hundred rounds, there was one instance of the slide locking back with one round still in the mag. She didn't even notice, just changed mags and I noticed the lone straggler still in the mag.

Took it out again today, and put another 200 through it. Had three premature slide locks (not all with only one round left, but all were with my FIL shooting - he does not lock is wrist very well).

The entire time shooting it, it would "stutter" like the slide went halfway, stopped, and then finished closing. It happened more with the short magazine than with the finger-extension mag, which leads me to think it was related to not being able to control it as well with the shorter grip. At first, I thought it was the round hanging up on the front of the feed ramp, but now I believe it is the slide lock trying to engage while firing. I think that because all of the "failures" have been the same slide lock, and not a misfeed.

So the question is, is there a fix for premature slide lock? Is there a stronger slide stop spring, or something to fix that? I searched, but it seems most people on here with that problem either deal with it or send it back to S&W. I thought by now there'd be a fix for that.

 

[comeandtakeit]

Did you try different types of ammo? Does your wife have a firm enough grip on the gun? Does the premature locking only happen when she's shooting it? Is her thumb hitting the slide lock during shooting?

 

[The Lone Haranguer]

Originally posted by comeandtakeit:
Is her thumb hitting the slide lock during shooting?

I would particularly wonder about this. It would be quite possible for a long thumbed person, using a very high thumbs grip (either with the shooting or support hand), to touch and push up the slide lock during recoil. I have not had even a hint of a malfunction with my 9mm compact, so this is speculation.

 

[the naked prophet]

She has particularly short thumbs. Nobody who has shot it has bumped it up. I have not had the malfunction happen to me. I would limpwrist her Colt 1911 Compact Officer, and she didn't. I am not sure she is limpwristing the M&P, especially since she didn't have a problem with her compact .45.

The gun should not be locking the slide back before the mag is empty. This is a gun problem, not a user problem. It has come up on here before, but I couldn't see that anyone had a fix for it except sending it in to S&W.

 

[wally]

Take the gun apart as if to clean. Reinsert the slide lock with the slide/barrel removed. Insert a magazine with three or four rounds in it. Slowly push the rounds out of the mag as if it was feeding the gun and look for contact with the slide lock lever or side to side wiggle of the rounds that could let them hit the lever. If the latter may be a mag problem, but usually its the slide lock lever is a little out of spec a bit too long -- usually you can see "brass marks" on the inside face of the lever where the bullets touch it.

You can use the brass marks as a guide as to where to file off a little material so the rounds stop touching it, or you can send it back to S&W, their warrenty service is outstanding.

--wally.