Glock 20 Gen 4 Problem

[PandaBear]

I have a stock Glock 20 Gen 4 with all of the up-to-date parts (extractor, RSA, trigger bar) and I am consistently getting failures to feed with ONLY the last round in the mags.

Total round count is close to 280.

The only ammo I've used is Underwood 165/180 TMJ and Underwood 150 JHP Nosler's.

It happens with all 3 of my blocked 15 to 10 round mags as well as my 10 round factory mag. They are all Gen 4 mags. Someone on another forum mentioned that they took theirs to a Glock armorer and the armorer said the mag springs were about an inch to short. He ended up stretching them out and his FTF's went down, but still wasn't 100% reliable. Another individual said they were having similar issues with their Gen 3 and replacing the slide lock spring and slide stop lever (I have the extended) fixed the problems.

[Carcassonne]

I don't understand what you mean by fail to feed by just looking at the pictures. Does the round jam against the feed ramp and stop the slide?

Have you only put one round in the magazine and released the slide, and does it jam that way, or only after it cycles from a previously fired round?



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[PandaBear]

It only happens after previously cycling a round. I've tried loading 2-10 rounds at it doesn't make a difference. Slide locks back as if mag is empty and last round fails to chamber. Looks exactly like the pics I posted.

[Oceanbob]

Have you changed out the slide release? Sometimes when you install the old or new slide release you install the bottom pin before the top pin. The end of that curved wire spring should be Under the top cross pin. Take a look. A weak spring will bump up the release and lock the slide.

Underwood is fast moving ammo. The mag spring has less tension on that last round and maybe the slide is moving too fast for the spring to raise the round up for chambering. I had a similar issue with my Glock 23 and hot ammo. I upgraded to Wolff Springs that were plus 10%. Problem went away.

Is the extractor clean.? Gunk in the extractor groove might be an issue.

Are you riding the slide and slowing it down?

Maybe with hot ammo a heavier recoil spring would slow the slide down.

Call Glock and explain this problem. They might have some upgraded magazine followers we don't know about.

Let us know.

[PandaBear]

The extended slide stop is installed properly and I don't think I am riding the slide.

When I push the follower down on an empty mag, I notice it gets caught a little on the front end as its returning back to the top. I'm going to sand it down until the follower no longer gets caught. I may even consider bending the top coil upwards to help give the follower an extra push towards the front if that makes any sense.

[5.56Geo]

The last round always seem to sit differently on most Glock magazines. What is the C.O.A.L. of the ammo you are shooting? It is very possible it is on the shorter side of the acceptable length causing the round to hang up on the bottom of the feed ramp as its being chambered long enough to have the slide run it over and not allow it to go into battery. The C.O.A.L. should be 1.250" to 1.260" anything shorter cause the type of issues you are having.

[PandaBear]

I don't have calipers to measure, but I don't think it's the OAL that is the problem. I went ahead and ordered a Wolff 10% spring for my 10 rounder.

[jeffafa]

Does it happen with both the TMJ and JHP ammo? There is an issue with 10 round Glock 19 magazines that don't feed the last round of JHP ammo, but as far as I know it fed FMJ without issue. As someone else mentioned, the solution was an upgraded magazine follower.

[PandaBear]

Yes it has happened with all 3 types of ammo I've used (2 TMJ, 1 JHP). I had some of the bad 2183 followers for my Glock 19 and Glock sent me new ones. As far as I know the 10mm followers should be alright, but I will double check.

[tonyxcom]

What is interesting to me is that the extractor doesn't appear to have grabbed the cartridge like it is supposed to, so something is out of time.

I had issues with my M&P45 failing to load on the last round that developed into FTF every 3 or 4 rounds. But in my particular case, the extractor was digging into the rim of the case and stopping the feed. I just filed that corner of the extractor until I stopped having feeding issues.

Came to suggest something along those lines but you have a completely different problem. The rounds should get pushed by the breach face while the round slides under the extractor. Your rounds are getting pushed by something before the breach face reaches the back of the round.

[mulyhuntr]

I have the same issue with my gen 4 g20 at times as well. It only happens with heavy loads and never when I have my .40 barrel in it. I'm guessing it has something to do with the slide velocity of the heavy 10mm loads. I put a 22lb recoil spring in it to see if the issue goes away, but haven't had a chance to test.

[Speedpower]

I'm Almost positive that the problem is in the magazine, if only there's a way to try a standard 15 round magazine

[PandaBear]

While there are certainly people who own Glock 20 Gen 4's without any issues, there are others just like myself that have FTF issues.

My factory 10 round mag and my 15 round blocked mags all fail to feed the last round after a previous round has been cycled.

A Gen 3 owner reported he was having the same problem as me and said replacing the slide stop spring and slide stop lever cured his FTF issues. I have done this and it has not cured my Gen 4 issues.

Ammo I've used is Underwood 165 TMJ, 180 TMJ, and 150 Sierra JHP's.

Total round count is around 270.

An individual on 10mmfirearms said he wasn't having problems with the 10mm ammo that was within spec, but as soon as he tried mid to full power loads such as PBR or Underwood the FTF issues began to show up. He sent his back to Glock and they sent it back saying they had tested it and that nothing was wrong. Turns out they apparently use CCI Blazer to test which to my knowledge isn't much more than 40 S&W.

In conclusion, I don't think the issue is with the mags or the ammo, but it's how the Gen 4 (stock) handles the mid to full power ammo such as PBR or Underwood.

I do know Glockmeister now offers Gen 4 recoil springs in heavier weights, but they are single captured instead of dual.

[the0thermrt]

same problem here in gen3 w/ DPM spring system. the Underwood rounds recoil hard and jolt the last round forward in the mag. the round tilts the follower so it hits the slide stop to hold open with 1 rnd remaining.

[Bill Steele]

same problem here in gen3 w/ DPM spring system. the Underwood rounds recoil hard and jolt the last round forward in the mag. the round tilts the follower so it hits the slide stop to hold open with 1 rnd remaining.

This sounds like the culprit.

I have run very hot loads, hotter than UW, through my G20SF and G29SF and never had any feed issues. I have used stock and 22lb RSA's, again no feed issues.

On a couple of other 10mm forums, a lot of guys seem to run into feed issues with the hotter ammo (Gen 3 and Gen 4). Some claim a heavier mag spring fixes things, some say a heavier RSA fixed their problem (less easy to see how that would be, just because felt recoil increases as RSA rates go up, although things are slowed a bit with the heavier RSA)

I would be inclined to pick up some extra power Wolff mag springs and give them a try (or double up on stock springs), maybe the higher rate spring will control that last round a little better, keeping it from sliding forward and causing the early slide stop engagement.

Good luck with the debug.