Slide locks back on last round

[Mairsil]

After nearly 6 months of waiting, I finally took my brand-new G20 to the range today. I absolutely love it! However, several times the slide locked back with one round still in the mag. Racking the slide didn't help, I had to push down the slide stop for it to close, so it wasn't my thumb riding the release (not very likely for a lefty like me anyway ;A). The round (Remington UMC) chambered and fired fine each time after I pulled down the slide stop.

I'm almost certain that I've read about this issue before, but I couldn't find the post anymore. I'm not too worried about it, but I'd like to know what is causing it.

My G20, while NIB, has been on the dealer's shelves for nearly 10 years (!!), so perhaps the spring has just aged. I haven't detail stripped it yet, so I haven't put the slide stop spring in wrong... :)

[bambihunter]

This topic should be within the last month here on the 10 ring so if you want to flip back the pages until you find it or search for it. Much has been written about it and I think the suggestions have fixed most people's problems with this matter. I personally haven't had it happen (knock on wood) so I don't remember the process or I'd tell you...

[duckslayer79]

I know I had a few problems like that with my mags. I had put well over 2000 rounds through the 6 that I originally had. My last round was locking back the slide almost every time. I took out my slide stop lever spring and compared it to a brand new one that I had. It ended up being that the spring was worn. Changed it and 500 rounds later its working great.


That should be your first thing to try. If that doesnt work then check the feed lips of the mags. If they are bent to far apart, then it could be allowing the follower to ride to high enough to catch the slide stop lever.


Take Care
"duck"

[deuce32]

i've got the same problem. 200rds with no hiccups. added a carver mount and all of the sudden "slide locks with one rd left". what gives?

[Belgian Blue]

Mairsil,

I had the exact same problem with my G20. I was using a heavier 22# recoil spring & tungsten guiderod. Several people thought it was the heavier spring causing the problem. Evidentally, this happens with box-stock G20s as well.

IMO, the issue is induced by the magazine follower bumping the slide stop. If you take an empty magazine, and insert one round in the top of the mag, you'll probably see that the portion of the follower which is supposed to contact the slide stop sticks up past the edge of the mag cutout by about 1/16" to 1/8". I think that under recoil, this is enough to bump the slide stop lever upwards if its spring isn't brand new and extra strong.

If the problem were due ENTIRELY to a weak slide stop spring, I'd think it would occur intermittantly with several rounds left in the mag. Instead, this problem happens ONLY with one round left in the magazine. By the way,I don't think that heavier mag springs are the answer either.

Perhaps as duckslayer mentioned, the feed lips are allowing that follower to ride higher with 1 round left in the mag. OTOH, I think the BEST solution is a redesigned follower which has a slightly lower slide stop shelf, combined with an extra power (+20%) slide stop spring. I think the latter is PARAMOUNT in solving the issue of what I call "Magnum Bounce"

What I did personally, is file about 1/16" off the magazine follower slide-stop shelf. (I had two 10rnd. mags) I haven't had a chance to try it out with Double Taps yet, but I will surely give a range report when I do. You might try a new slide stop spring as mentioned above. Like I said, I wish Wolff could make an Extra Power slide stop spring.

Belgian Blue

[Medpilot 2]

My 29 has done this a few times, mostly with really hot loads. I'm thinking that the recoil is so great that the last round rides up from momentum enough for the slide-stop shelf to ride up along with it to stop the slide.

I think Belgian Blue has a good idea with filing 1/16" off the magazine follower slide-stop shelf. I believe that would fix our last round slide lock problem.

[Mairsil]

Assuming this is the slide-stop shelf we're talking about (not 100% sure... My first Glock :)), I can see quite a difference between my two mags.

http://www.neon-wonderland.com/zooi/20040918-5.jpg

I've marked them with a sticker so I can tell them apart. If the one with the high slide-stop shelf is the only one having this problem, I'll try filing it down a bit.

Thanks for all the quick and insightful replies!

[Medpilot 2]

After closer inspection, I'm not sure if cutting down the slide-stop shelf would help. If you insert your magazine with the slide off, you can see there is already a lot of space space between the shelf and the slide catch lever.

Yes, I know my gun is dirty. :cool:

http://www.iownjoo.com/freeimghost/medpilot/IMGP1472.JPG

[Belgian Blue]

Mairsil & Medpilot2,

Those are some excellent photos. Yes indeed that's precisely the 'slide-stop shelf' I'm speaking of. What got me thinking was my G22 with preban 15rnd mags has NEVER had such an issue in nearly 10 years of shooting, even with hot CorBon ammo.

I did the same thing to examine my G22 mag, I loaded one round into an empty magazine and the slide-stop shelf is actually at the SAME height as the cutout in the mag body with one round inserted.

From there, I suppose two factors are likely. The feed lip width, and the height of that shelf on the follower. As cheap as magazine followers are, I thought it would be worth a try.

It is true, on my G20, that there does seem to be enough room between this shelf and the slide catch, but I'm thinking under recoil, combined with the slightest frame flex, it just might make contact. I can't wait to give it a try with my next order of Double-Taps.

Belgian Blue

[Belgian Blue]

Here's a stock G22 PreBan magazine. Note the location of the slide-stop shelf:

http://www.parkcitiestactical.com/album/00001588/Glock_Mag.jpg

As you can see, the G20 mags have quite a bit more material ABOVE the cutout in the magazine tube. This mag has been through years of use and has never had any pemature slide lock.

Belgian Blue

[Medpilot 2]

Belgian Blue,

My G23 mags (preban) look like your G22 mag in the picture with one round.

It will be interesting to see how this turns out.

[duckslayer79]

Im curious as to if the followers are riding to high due to the material or cause the feedlips are out of spec?


Take Care
"duck"

[Medpilot 2]

duck,

Did you ever figure out your light primer strike problem?

[duckslayer79]

Originally posted by Medpilot 2
duck,

Did you ever figure out your light primer strike problem?

Ah crap, I forgot to post about that.;P Yes, it was the channel liner all along. I ended up getting a whole new gun minus the frame, barrel and slide for free, trying to figure out the problem.;f


Take Care
"duck"

[Mairsil]

Originally posted by duckslayer79
[B]Im curious as to if the followers are riding to high due to the material or cause the feedlips are out of spec?

Mij feed lips measure .375" and .379". A bit wide, but within spec according to CGR (http://www.custom-glock.com/magtech2.html).

[G-20er]

I would like to hear more about what you guys find out. Hope you get to the bottom of the problem.

Just for info...this last weekend was the first time I have shot over 250 rounds since I changed a few parts on my gun. As you may recal on a previous post, my G-20 was doing the same thing with the slide locking back with one round remaining in magazine. I took out my 22 pound recoil spring and installed a 20 pound recoil spring and I also reinstalled the factory extended slide release arm. After shooting over 250 rounds the only problem I had was 1 light primer strike. Probably my fault from not seating that 1 primer deep enough.

Anyway it was a real relief to see the gun work flawlessly once again. Can't really say what 1 of the fixes took care of the problem, since I changed out both at the same time, but it also may have been caused by both of the components...who knows, but for me it took care of my problem and I was shooting loads hotter than most will get to try. So if it can handle that without problems, I'm sure all other ammo will do just fine.

You may be onto something with the mags bumping the slide release, it also may be caused from your left grip being slightly under the magazine and during recoil the mag gets slighty pushed up to make your clearances non-existant, thus hitting the slide release button. I say this because I did change my grip recently for more accurate shooting and now my left hand does not go under the mag. This could have taken care of the problem also. I now lock two fingers of each hand in front of grip and sandwich the sides of grip only...my accuracy has improved dramatically.

Please let us know what you find out.

[yotehunter]

I also have the same problem with my G20. I took it out today and had one round FTE and the slide locking back with 1 round in the mag. I have a stainless guide rod and 22# captured spring installed. This only happened when I used Double Tap ammo. I also used some Blazer and Corbon with no problems.