View Full Version : Slide fails to lock back

June 25, 2010, 20:41
I haven't cleaned my 17 in about 1k rounds or so. I just picked up some Brown Bear from Aim and about 100 rnds into it, the slide keeps failing to lock back on an empty mag. So, is it the dirty gun or the ammo? I know, I can clean the gun, but I wanted to see how long I could wait to clean it. Also, I know I can try brass cased ammo tomorrow and see if the slide behaves similarly. I'm shooting an IDPA match Sunday, so the failure to lock back is a big disadvantage. What are your opinions? Just curious.


June 26, 2010, 03:07
1k is nothing for a broken in Glock.

How many rounds through it?

Does it do this with every mag?

Armorer's manual sez:

Magazine follower broken
Dirty magazine
Weak magazine spring
Worn slide stop lever notch
Dirty gun (hehehe)
Needs lubrication
Deformed magazine
Trigger pin inserted too far (left or right), Slide stop lever worn
Slide stop lever is damaged
Underpowered ammunition (sometimes the Russky stuff is underpowered)
Shooting with an unlocked (limp) wrist
Improper grip

Do try quality factory loads from Winchester, Speer, etc.

Try having someone else shoot the pistol.

June 26, 2010, 10:22
Thanks for the info. I just shot a 3 gun match with it last Sunday and no problems using PMC brass cased. It locked back on the first few mags of Brown Bear, but then only did so intermittently. It seemd the ammo was ok power wise just by feel. I am going to try it side by side with brass cased and if it still does it, I will clean it tonight before the match tomorrow. It has 6 or 7k down the tube.


June 26, 2010, 12:11
Well, I took it out today and tried one round in the mag and then two (same mags I used yesterday) and the slide locked back every time. I'm perpelexed. I'll probably clean it tonight just to be safe.

June 26, 2010, 15:43
CHeck the mag springs to. I have had some that act like that on weak springs:fal:

June 29, 2010, 17:06
Cleaned it. It doesn't fail anymore...I guess fouling can affect function. I shot a classifier, IDPA match, and two-gun side match with not so much as a hiccup. Thanks for the replies

June 30, 2010, 12:58
I've had this problem before but only with the cheap range mags of KCI...and never ever with Glock oem mags.

I always make sure my "range" mags stay far away from my Glock oem's so as not to get them mixed up!

June 30, 2010, 16:53
Well, it started again after only 150 rnds or so. I'm thinking maybe mag springs, but don't really know. Maybe Rusky ammo, but it doens't FEEL underpowered.

These are Glock OEM mags and are maybe 3 years old at most, but I do use many of them frequently.


June 30, 2010, 17:48
Make sure the slide stop lever spring "leg" is correctly installed. It should be compressed between the bottom of the top pin.

Verify there's a positive "downward" force holding the slide stop lever against the stop if the receiver.

The armorer "test" for the mag spring:

Drop the magazine from the pistol.
Rack slide several times to clear the chamber.
Check for clear chamber visually and digitally (wif yo finger), twice.
Drop slide on empty chamber, insert empty mag.
Rack slide as violently as possible to the rear. Ensure slide locks back every time.
Repeat several many times for each (empty) magazine you have.

When testing as above (or shooting), does it fail to lock back intermittently or consistently? With only one of the mags? Or randomly with any mag you have?

If it fails to lock back with all mags makes it unlikely that it's a mag spring issue...

Let me know what happens. I might have an extra mag spring or slide stop lever I got for free. Same price to you.

June 30, 2010, 21:43
A possibility, that I have experienced, is stout ammo combined with weak springs. IF the ammo is stout, the slide may be closing over the follower before it has a chance to rise all the way to the top and make contact with the 'stopper thingy'. Highly technical I know. Get some federal hydrashok. It is supposed to be subsonic and so it should slow the slide action down slightly, allowing the follower time to engage. Just to see if that is it. The cheap ammo may be loaded a lot hotter than other ammo that is made to more stringent quality standards. The fix is new springs and better ammo.

Another possibility not mentioned is your hand position. when the pistol recoils, does any part of your thumb make contact with the slide lock? If it does you may not realize it. Especially if it is intermittent. Check hand position and if it is close, change it just for experimentation and shoot a bunch of rounds. Not for target, but just to see if positioning/grip is the issue.

Hope this helps. It looks like most of the other stuff has been covered.
BTW,.. if it happens to be a magazine issue, mark it and keep it so you can practice your tap, rack, bang drills.