Hey Guys!  I’ve got a Gen 2 G19, and the slide will not lock back automatically after I fire my last bullet.  It will lock back if I have an empty magazine and I pull the slide back.  Just not when shooting.  I’ve tried a new magazine and it does the same thing.  

What is the common cause for this?  A slide release?

Thanks!

"Limpwristing"

Drive the pistol into the target.  Don't let it do whatever it wants during recoil.

Could be the slide release since its so old. I mean I bought my first Glock in 1990 and it was a gen2 19.

Pull the slide off and insert an empty mag into the frame and make sure the magazine follower is pushing up on the slide release.

Check your grip. It’s possible that you’re riding the slide stop with your support hand. If that’s the case then you can change your grip, or just know that’s what happens and be prepared to change mags that way always. People do both so if you’re really happy with your grip it’s not a deal breaker. I had an issue with it before finding a grip that was more efficient and better suited me.

Edit: Kagwerks made a slide stop lever that sits higher to address this very problem. Could be a solution for you.

Could be release. Could be operator.

If you're using this gun for HD or defense period,
replace the release if it has never been done.

I've got a few gen 2 G19's. There is a decade span in production
and a 'update' of the 'black' parts not mention the length of time
it's been since one was made.

Change out part if it's not involved in a "collection"
needing to maintain it's originality.......if so, your task
is to locate a NOS part or functional take-off from donor gun
to maintain a functional collection.

ETA: replace and re-evaluate. These guns are at 20-30+ years old
now depending on production date.

I’m going with worn out parts.

Step one shoot it left handed with one hand
If it locks back properly it is your grip end of story. Only if this test fails do you consider parts replacement.

If the slide does not lock back when manually cycling with an empty mag inserted, there are generally two reasons.

1: If the gun is a 3-pin frame, make sure the spring for slide stop(it's not a slide release, it's job is to stop the slide when empty) is below the locking block pin.  If above it, the spring won't push the lever to contact the magazone follower.  If this is an older 2-pin frame, this is not the problem.

2: If it's not the slide stop spring placement, it's ALMOST ALWAYS worn a worn out magazine spring.  They don't have to be horribly weak, just enough and they won't push the follower up far enough to engage the slide stop lever.  It's an incredibly common and more often than not overlooked failure point

Springs are cheap, always have spares on hand.  I usually get the Wolff Gunsprings 3 pack from Brownell's.

If you've installed a mag extension and didn't use a longer spring, this is in effect the same thing as a weak spring.  Any company that says their + whatever extension doesn't require a longer spring is WRONG.  Anytime you change the length of the mag, you need to change the length of the spring, it's pretty basic.  That's why all the real companies that sell extensions either include or recommend a spring upgrade.  If they don't either include or recommend a spring, I move on.

Adding a +2 to a G19 mag?  Use a factory G17 spring or an upgraded spring.

A good way to verify if it is indeed the sriing that's the problem is to remove the spring, stretch it out, reassemble the mag and try again.

Also be sure to check the followers and make sure they aren't worn down.  It's rare, but it can happen.  It's a plastic follower engaging a steel tab on the slide stop.

When I replace mag springs, I update the followers if they need it.

If you ever get a chance to take the factory Glock armorer's class, DO IT!  I thought I knew everything there was to know about Glock handguns, but oh boy, did I LEARN A LOT.

Good luck!

I just watched a video addressing this yesterday. Not sure how Arfcom feels about Johnny Glock, but here it is.