Glock malfunction question

[dmaxfireman]

So my buddy has a G34 Gen5 with RMR, gun started out completely stock with weak extraction, the occasional brass bouncing off the forearm but zero BTF. In 3 of my personal Gen5's I have added a non-LCI SLB and it greatly aided in extraction with no other problems.

In his G34 with the non-LCI SLB we have roughly 50-60% light strikes per mag. WWB ammo. The rounds that fire extract wonderfully.
When we switched back to the LCI SLB we had zero light strikes the extraction went back to weak but still no BTF.

Now the questions, has anyone ever seen this before? Why would a Gen5 26/19/17 not have this problem but a 34 would?

Yes I understand that Glock does not recommend the interchange of these SLB's just trying to figure out what mechanically is happening to cause this.

[26 Inf]

The non-LCI SLB is thicker and places more pressure onto the back of the extractor. While I'm not sure if the extra pressure drives the extractor forward, I am certain it hols it in place more firmly.

Unlike the M4, where the extractor actually snaps over the case rim, when you pistol feeds and chambers the case rim slides under the extractor.

So, a couple of questions - is your bud's pistol and MOS, or one who someone did and RMR cut for? How many rounds through pistol, specifically on the recoil spring?

If I had access to the rounds that failed to fire, I would look to see where the 'light' hits are located on the primer. I believe that there is a good chance they would be slightly off-center as a result of the pistol not being fully into battery when fired.

This could be caused because of the extra pressure exerted by the extractor as the round slides up the breech face slowing the slide enough that it doesn't come fully into battery.

I'm not a big believer in the Glock BTF, simply because we ran nearly 200 students a year through our courses with Glocks. When the BTF problem occurred it was with shooters who had fundamental issues. The problem magically disappeared when the shooters became more fundamentally sound.

I'm not infallible, just reporting my experiences after about a quarter century of training shooters with Glocks.

[dmaxfireman]

It is a factory MOS model. It has 1-2k mixed ammo through it. The failure to go into battery makes much more sense than a hang up of some sort on the striker plunger safety.

I'm going to borrow it and see if I can get more specifics on exactly what is happening with the failures and post back with some pictures.

[CoryCop25]

I have totally stopped using WWB ammo.
This could be the problem.

[dmaxfireman]

I have totally stopped using WWB ammo.
This could be the problem.

This was my initial gut instinct as well, but as soon as it was switched back to a short SLB the light strikes were gone for the rest of the session. No other parts were changed.

[CoryCop25]

WWB primers tend to be very hard.
I have also had issues with 124 gr. ammo in my Glocks.

[Joe R.]

Winchester White Box is notorious for it's unreliability. Try different ammo and see what happens.

As far as 124 gr ammo in Glocks, it's pretty much all I use. Lets face it, the gun was designed initially as a military arm. 9mm NATO ammo is a hot 124 gr load. I've used 124 FMJ for practice and Federal 124 HST for duty for years with good results.

[ST911]

Likely: Longer, heavier, slower slide + added extractor tension creating a lockup/OOB issue.

WWB isn't just the 115 FMJ value packs anymore, OP can you verify which WWB product you're shooting? If it's the 115 bulk, that ammo is already pretty light, exacerbating the above. G34/17L can be a little wonky with light economy loads anyway.

Glock spec'ed an SLB for each extractor for reason. Put the right one back in the gun, shoot better ammo.

Re: 124gr bullets. Bullet weight as a variable has almost nothing to do with anything.

[dmaxfireman]

Likely: Longer, heavier, slower slide + added extractor tension creating a lockup/OOB issue.

WWB isn't just the 115 FMJ value packs anymore, OP can you verify which WWB product you're shooting? If it's the 115 bulk, that ammo is already pretty light, exacerbating the above. G34/17L can be a little wonky with light economy loads anyway.

Glock spec'ed an SLB for each extractor for reason. Put the right one back in the gun, shoot better ammo.

Re: 124gr bullets. Bullet weight as a variable has almost nothing to do with anything.

I get it, that's why the original SLB is back in it. Just trying to learn what is going on to cause the malfunctions. The ammo is 115 bulk pack.

The slow slide speed makes sense to me, causing the fail to go into battery.

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[ST911]

That ammo is generally weak and inconsistent, and is stacking the tolerances enough to stop the gun.