What is causing slide to stay open?

[Prophet]

If: Shooting a glock 23 with a full 10rnd mag, every 3rd round the slide locks open. What causes this?

Thank you for you help

[MA2]

Weak/worn out slide stop spring.
Field strip, and manually lift up the slide stop, it should go back down under spring tension.

If not that, than a high thumbs forward grip...your thumb.

[SDM44]

Also make sure the stop slide spring underneath the rollpin, and not over it.

If you've changed out the slide stop before to say an extended one, you'll know what I'm talking about. If the spring is over the rollpin, it'll naturally want to push upward on its own. If it's under the rollpin, like it should be, the slide stop will naturally want to fall down under tension when you lift it up... the correct way.

If the spring is under the rollpin, you can take out the slide stop and lightly pull up on the spring to 'extend' it a bit and then put it back in so so that there's more tension when it's back in place. Probably the first thing I would try since it's free & easy to do.

[003]

Was the gun recently disassembled? If the locking block pin is under, as opposed to being above the Slide Stop Lever Spring the Slide Stop Lever will not function properly.

The locking block pin must be installed first - - first pin out/first pin in. Then the slide stop lever is installed. That way the Slide Stop Lever Spring is under the locking block pin.

[Prophet]

Thank you for the info; much appriciated.

[HighLander51]

You are riding the slide stop with your thumb. If the spring was in wrong (on top of the small pin) it would lock open every time.

[RuggedJay]

Operator error. Nothing wrong with the Glock.