Glock Slide Problem

Could be a number of things

-weak magazine springs
-different grip, you might be hitting the release
-spring for the release may not be installed correctly
-etc

When was the last time you detail cleaned it?

From a gunfighting perspective, this is one reason to put your slide in battery BEFORE you load your pistol to train yourself to apply the extra force required to seat the magazine when the slide is not locked open, such as what happened in the OP's situation or when you seat a fresh magazine after clearing a doublefeed.

I use the tasks of loading and unloading as a training opportunity to exercise the same skills I have to use to clear stoppages. When I load my Glock 19 I always put the slide in battery before I install a loaded magazine. After I seat the magazine I roll the pistol to the right about 90-degrees while simultaneously racking the slide to chamber a cartridge. Then I perform a Tactical Reload.

Care to elaborate anymore?

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When the slide is in battery the top cartridge in the magazine makes physical contact with the bottom of the slide. When you seat the magazine the top cartridge is pushed farther into the magazine against the resistance of the magazine spring.

When the slide is locked open you do not encounter this resistance.

In a defensive shooting, if you shoot your gun dry and the slide fails to automatically lock open or you had to clear a doublefeed, then the slide will be in battery and you will have to exert more effort to seat the magazine to recover from this situation.

Shawn Dodson said:

When the slide is in battery the top cartridge in the magazine makes physical contact with the bottom of the slide. When you seat the magazine the top cartridge is pushed farther into the magazine against the resistance of the magazine spring.

When the slide is locked open you do not encounter this resistance.

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You're right. Especially noticeable on a full magazine, not as noticeable if only filled half way or so.

what kind of ammo?

If you insert an empty mag and manually rack the slide, will it lock back?

The front left corner of the magazine follower, under magazine spring pressure, engages the slide lock when the last shot is fired.

I suggest you inspect your magazines to verify the front left corner of the magazine follower is undamaged. (There is a molded notch on the front left corner of the follower. There may be a number imprinted on the floor of the notch.) You can damage this area if you slam an empty magazine home.

With gun unloaded and the slide locked open insert an empty magazine. Just before it seats look through the ejection port to see where the internal "tab" on the slide lock engages the notch on the follower. After you seat the magazine, release the slide lock to put the slide in battery then slowly retract the slide, and while looking through the ejection port, observe the interface between the magazine follower and the slide lock tab for proper operation.

You mentioned the problem occurred with two magazines. Are these the only magazine you have? Have you cleaned them? If not there might be enough grime in the magazine tube to retard the movement of the follower and it either moves up too slowly to engage the slide lock before the slide is propelled into battery by the recoil spring, or the follower could be seizing in the magazine body.

Good luck.

Is this one brand and type of ammo?

Could it be a weak lot of ammo? Years ago when working up some 115 Gr handhoads for my G17. I found that a certain charge was enough to cycle the slide that it shot fine. But as it turned out it was slightly short stoking the slide just enough that it was not locking the slide back on the last round. Going up just .2 of a grain cured the problem.

The longer heaver slides of the G17 and G34 seem a little more prone to this issue especially with weaker 115 Gr loads.

Do you have big hands? And point your thumbs forward? Because that might cause you to hold the slide release down after you shoot your last round. Happens to me once in awhile.

S&B. But I've shot hundreds of rounds of this stuff without problems

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I'll echo Runningman, have you shot this particular box of ammo without incident before? I would pick up a different brand of ammo and run it through your gun just to pinpoint or eliminate ammo as a problem.

Edit: Nevermind, not too quick on the draw tonight.

I have shot hundreds of rounds of this ammo (bought 1k last year)

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JoeMal, if the slide locks back when you manually rack the slide with the empty magazine inserted (meaning your magazine springs have enough tension) and if the slide does not lock back when a round is fired, then it's:

1) Slide is not moving back enough when the last round if fired for the magazine follower to push up on the slide lock
2) There's obstruction/roughness towards the top of the magazine tube (inside) that is hanging up the magazine follower to move all the way to the top when the last round is fired.
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1) Since you are shooting the same ammunition that you shot in the past, can you verify that you have the same lot number of bullets? If you have more than one production lot in your 1000 round purchase, it may explain the difference in bullet performance. Are you are able to borrow or use the range rental Glock magazines? If the slide not locking is repeated with other Glock magazines, then it may be the ammunition lot. If the problem goes away with other magazines, then the problem is with your magazines.

2) Take apart your magazines and inspect the inside of the magazine tubes for any debri or roughness near the top of the magazine that might hang up the magazine followers. If the magazine parts are serviceable, clean and reassemble. If you think the magazine spring tension is weak, you can test this by adding cut pieces of cardboard to the base of one of the magazine (3 or 4 layers below the spring) to increase the tension. If the magazine with cardboard pieces locks the slide but the other magazine won't, then you need to replace the springs.

Magazines look fine, ammo as well.

I've seen this a couple of times.. Get someone to watch your thumbs when you shoot. I think your riding the slide stop a bit and that's the hang up.

Remove the slide and clean the slide lock as well as the area around it, both internally and externally. There could be some grime that's retarding its movement. Because you're experiencing problems with both magazines I suspect the problem to be here.

Your magazines, although showing some wear, appear serviceable.

Here's a YouTube video with Lenny Magill demonstrating how to disassemble/assemble a Glock magazine: http://www.youtube.com/watch?v=uB28dFAMVQc

After putting at least 10,000 rounds through a Glock 34 I have learned some things:
1. With good ammo the gun will function as designed if you put it together correctly.
2. With good ammo the gun will function as designed even if you think you are a gunsmith and change some things.
3. With good ammo and not riding the slide stop/release the slide will always lock open.

My suggestions:

1. Buy/try a new box of ammo, name brand, yes I know you have shot XXX rounds of the S&B, just make it easy and eliminate the ammo as an issue.

2. Shoot it left handed only, this will tell you if you’re riding the slide stop/release.

The "insert mag on a closed slide" discussion was interesting though having nothing to do with this OPs question.

My definition of interesting in this case = one mans opinion.

But then again, all this free advice, including mine, could be worth exactly what you are paying for it.

I would say load up a round of heavier bullet into the mag first and see if it locks the slide back, when I shoot 115gr UMC my glock short strokes a little and even though you say it isn't the ammo, I think it really is. Your magezines are fine.

Regarding the mags, they may or may not be the problem here, but you seem to be averse to buying new mags. Mags wear out, just adjust to that fact. Glock mags are under $25.