My wife has a second generation Glock 23 she had owned for some time and was having issues today at qualifications with many failures to feed. She's an experienced shooter and going back into law enforcement, so no she was not limp wristing it. The only new thing is some of the magazines - I purchased some of the newer FML drop free magazines with the #8 follower and ambidextrous cut in the magazine. Are the newer Glock magazines known to be problematic in older Glocks? I'm pretty sure her original mag for the gun functioned fine and that it was all the newer mags causing it to stovepipe. (The ammo she used was also used by another shooter today using a Glock but with no issues in that pistol.) Is there an easy fix with maybe a #5/#6 follower and/or aftermarket springs? Thanks for any input - trying to avoid buying new mags and I'm sure someone here has dealt with similar issues before.

Find her some OEM  mags. Newer mags will work fine.

Some of the newer .40 magazines can cause failures to feed. In particular magazines with #8 followers that have 1 or 2 marked on the bottom of the back of the magazine tube. Some of the early ones with #9 followers can also have this problem. The problem is that Glock made the little protrusions of plastic at the front of the feed lips too big, they slow the rise of the top round and cause a failure to feed. The solution is to shave those protrusions down until the FTF's stop occurring, and perhaps a little more after they stop occurring just to be sure there won't be any problems in the future. You can remove those protrusions entirely and it won't cause any problems. Here's a picture showing one of those protrusions, there's one at the front of both feed lips. Nevermind the instructions in the picture, just shave them down until the FTF's stop.

Magazine issues not withstanding, how old/round count is the recoil spring?

Mags are OEM and were purchased new or like new, low round count - I think the issue is with the follower - I'll try this approach at shaving it down or look for older followers in lieu of that. Thanks for the technical help Voyager4520 and everyone else's feedback

Thanks for this post.  I'm having the same problem with mine.  FTF occurs with my newly purchased mags.  #9 followers.

I was losing confidence in my gun.  Hopefully this is the fix.

This Glock my wife has was her duty weapon for three years - she shot it at the academy and with her PD extensively - never ever had a problem. After she left her job, the PD got newer Glocks and she purchased her old Glock from the FFL but did not get her old magazines with it. I plan to modify some of the followers soon and see what happens but I know the issue is in the new magazines. My wife is going back to work part time as a reserve and thankfully she qualified fine with multiple FTF on her range day.

I had the problem myself with two magazines, one with #8 follower and "1" mag tube, and another with #8 follower with "2" tube. Shaving down those plastic protrusions fixed both of them.

The followers aren't the problem. With .40 magazines, tubes that originally came with followers #1(marked 1028) through #5 can only use one of those followers. Tubes that came with #6 through #8 followers can use any of those followers. Tubes that came with #6 through #8 followers are supposed to be able to use #9 followers, but the #9 followers are wider on the part that engages the slide stop and they may fail to rise fully in the tube causing a failure of the slide to lock back. If that occurs you should see a rub mark on that part of the follower and you can shave it down until the empty magazine reliably locks the slide back. Here's the area of the #9 follower you may need to shave down to make it work properly in a tube that came with #6,7,or 8 followers:

Interesting.  Does Glock publish this information somewhere?
For my G23, I have 8 mags.

1 mag:  unmarked body, #8 follower
4 mags: #1 body, # 8 follower
3 mags: #2 body, #9 follower

Do I need to modify all of them?
The only ones I have shot for sure are the #2 body, #9 followers.  I had frequent FTFs.

The only thing Glock publishes is what followers you can use in which magazines. They do not admit to any problems with their magazines. The people in Smyrna may not even be aware of the plastic protrusion problem but the people in Austria certainly are because they changed those protrusions to be smaller on the newest magazines.

You only need to modify the ones you've experienced failures to feed with. You can remove those protrusions entirely and it won't cause any problems, even on a magazine that has never had that problem. The worst that may happen is that the follower would stick a little bit at the top of the empty magazine, but it would still lock the slide back reliably. Those protrusions act only to stop the follower at the top of the tube and prevent it from sticking slightly at the top.

I have never even heard of this. Is this situation more prevalent in .40 or does it happen with other calibers as well. I have never been a big fan of 40 and have run tons of 9 mm and 45 of all generations and never had an issue.

Sorry double tap

Modified the feed lips on one of the mags today (#2 body with #8 follower). My wife only put 10 rnds through the mag but no FTF this time. We'll troubleshoot each mag one at a time and mark them to ensure there are no more issues. Thank you guys for all the advice.

Just another field report. (Pardon my late response, life gets a little crazy.) My wife has used her other two duty mags that I also modified in the manner listed above. She fired in a night shoot with fully loaded mags doing various drills with no malfunctions, no failure to feed or other mag related issues. The modification worked great using a razor blade and a couple small files on the magazine body and I didn't have to buy new mags. Definitely worth the time and she has peace of mind with her Glock.

Thanks for the update.  I'm going to mod my mismatched mags right now.  I'll report after I've had a chance to shoot (in a few weeks).

I modded my mags by removing the nub completely.
Just finished a 3 day class.  No failures of any kind.
Looks like it worked.  Thanks for the info.