[tonyparson]

Assuming you're not riding the slide release lever with your thumb.

Possibilities for slide failure to lock after last round.
1. operator thumb
2. defective slide stop lever
3. worn follower
4. worn magazine spring.

You can check and eliminate 2, 3 and 4.
1. Unload your pistol and all magazines
2. insert empty magazine into pistol
3. Pull back slide all the way and let it go
4. repeat several times with each magazine
If it locks back every time, causes 2, 3 and 4 are okay

And welcome to GlockTalk.. :wavey:

 

[bentbiker]

You can test #1 by inserting one cartridge in a magazine and firing left-handed. Repeat ten times. If it locks back all 10 times, then you have been hitting the slide stop lever with a thumb during recoil.

 

[Twiglock]

Thanks guys, I will try both tomorrow at the range and report back.

 

[dsk]

I know I have a bad habit of letting my thumb impede the slide lock when I shoot my G19. I've never blamed the pistol for it. Unfortunately many of us are accustomed to using a high thumb grip from many years of shooting 1911 pistols.

 

[21Carrier]

I bet you are riding the slide release lever. I thought I was doing this with my G29, but now I'm thinking it's just a worn magazine spring. I ordered new ones. That magazine has about 6,000 rounds through it, so I guess it's about time. That's 600 loadings.

It can be hard to diagnose things like this that occur during recoil. When I was new to guns, I bought a Springfield XDm 9mm 5". The magazine kept dropping out while shooting, and I was SURE that I wasn't hitting the button during recoil. I tried changing my grip and all. It kept falling out. I took it back to the gun store, and they told me to try with my left hand. Damn, I felt stupid. I never could shoot that gun comfortably without hitting the mag release. It got sold.