I have a 1st gen M&P9 that the slide doesn't want to stay open after the last round. Pull the slide back on an empty mag and it stays open. When I got the gun it functioned properly and always locked open. The problem started after the last time I cleaned it and the mags, 4 of them. Ever since then, the slide more often than not does not want to stay open after the last shot, doesn't matter which mag. Any ideas what the issue is?
Slide won't lock open
- Thread starter Joe549
- Start date
The slide lock is a function of the magazine, unless you manually raise the slide lock.
Take the slide off of your M&P and then insert an empty mag, note the slide lock catch on the left is raised by the magazine notch on the follower via a metal tab that is part of the slide lock bar. Check that the metal tab is connecting to the magazine follower notch, if so but it isn’t raising enough, then the mags may not be seating properly or the follower is jamming and not raising fully in the magazine.
Take the slide off of your M&P and then insert an empty mag, note the slide lock catch on the left is raised by the magazine notch on the follower via a metal tab that is part of the slide lock bar. Check that the metal tab is connecting to the magazine follower notch, if so but it isn’t raising enough, then the mags may not be seating properly or the follower is jamming and not raising fully in the magazine.
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Common problem... if the spring on the slide lock is good and your buffer spring is not binding and your gas block is properly aligned and there is no obstructions at the port then a bit of material might have to be removed from the slide lock lever. We use to do this for roughly 10% of the C7s that comes across my bench. I just use a bench grinder and remove roughly 30 thousandth by eye.
Mags are back together properly. The slide will lock properly when manually operated on an empty mag, and the occasional last shot.
I don't believe so...
Same ammo, factory CCI Blazer 115gr
This is the M&P pistol, not the AR...
This pistol reminds me alot of a Glock, I looked at some pics online and I'm guessing it a mag issue? , unless you removed the slide stop and didn't install it correctly?
I'm just wondering?? if the mag springs install a specific way like a SIG 226? or they aren't positioned correctly in the mag body?
So just to clarify, slide looked back every time on an empty mag, and manually, but since you cleaned the pistol and mags it doesn't? did you do more than a field strip? and did you disassemble all the mags completely?
I'm just wondering?? if the mag springs install a specific way like a SIG 226? or they aren't positioned correctly in the mag body?
So just to clarify, slide looked back every time on an empty mag, and manually, but since you cleaned the pistol and mags it doesn't? did you do more than a field strip? and did you disassemble all the mags completely?
Prior to cleaning the mags, the slide always locked back after last shot. Since cleaning the mags, it usually does not. When cycling it manually on an empty mag it will stay open, even when cycling a dummy round through. Same result with each mag. I did not do anymore than a field strip on the gun, but I did dissemble the mags completely.
So far, the only conclusion I've been able to come up with is that my thumb may somehow now be pushing the slide lock lever and preventing it from lifting. I can't confirm this until my next range trip obviously...
Ya it sure is, however, he's talking about a 9mm Smith and Wesson Pistol, not an AR type rifle.
Scott
OK, sounds like it could be the mag springs? how old are the mags? , if you are "riding" slide lock lever that's a "you" problem. Since it locks the slide open on an empty mags sounds like the follower is OK, and when there is only one rd in the mag, it's able to do the same. When the mag is filled with rds, the spring, stays compressed somewhat and doesn't move the follower into position. That's my best guess from here?
He says slide locks back when manually manipulating the slide. Slide no lock back when gun goes bang. Probably a thumb issue.
I had this exact problem with my FMK. The problem was not enough oil, the gun wasn't cycling far enough to catch the slide lock. When manually operating it it functioned fine but while shooting it wouldn't always lock back.
Another possible option is the magazine follower is not coming up fast enough to catch the slide, which again could be an oil problem except with the mag, however I have troubles believing 4 mags would all exhibit that issue.
Another possible option is the magazine follower is not coming up fast enough to catch the slide, which again could be an oil problem except with the mag, however I have troubles believing 4 mags would all exhibit that issue.
He also said it worked 100% before he took the mags apart, hence the comment about check the mags.
Not hard, install a empty mag in the gun and it should push the mag lock up. slide off , than you can see what is happening.
Take the gun apart and check the amount of wear on the slide lock - if you've got a gun with a high round count (30K plus), the slide lock can wear. If that's not it and you're between 5 and 10k, replace your mag springs, also check for rounding on the followers - they're quite soft and they can be replaced at the same time as the mag springs. Also, while they may work for a while, low power rounds are not what the gun was designed for, if you're handloading, use a fairly stiff load. Lastly, check for your thumb overlapping the slide stop.
- Location
- West Quebec
I would try a new mag just to prove it...
I've done this, everything appears to be operating properly. The mags were also put back together properly. I cleaned it again, paying special attention to the slide lock lever in case there was some crud built up around it that may have been interfering with it. So far the only thing that seems to be the possible cause is that I have somehow changed my grip and my thumb is now interfering with the stop lever..
