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cohland

G34 POI Problem and Solution

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Problem

My new Glock G34 Gen4, test-fired at the factory on June 4, 2013, was shooting about 4” to the right at 20 yards when delivered. I call this the “G34 POI Problem”, where POI stands for Point Of Impact.

This G34 was delivered with Glock Night Sights, and the rear sight was centered on the slide, so that wasn’t the cause of the POI problem. I looked for any damage to the barrel crown and found none, nor was there any other obvious defect in the gun. It just liked to shoot to the right.

I ordered an adjustable rear sight that would enable me to move the Point Of Aim (POA) to match the Point Of Impact (POI). I installed the sight, being very certain to center it on the slide, thinking that a simple misalignment of the original sight might have caused the problem.

To align the POA with POI at 20 yards, I had to make an adjustment of six clicks of left windage, overcoming the pistol’s tendency to shoot to the right. That was all of the adjustment that was possible, and the POI was still off a bit.

The pistol has been fired in two matches with these sights, and it now hits where it is aimed with the rear sight adjustment. However, it still bothers me that the POI is so far off, and I probably can’t use a fixed rear sight on this gun until I solve the POI problem.

After reading a number of postings on another Forum about new 9mm Glocks shooting to one side or the other, I began to wonder if there really was a problem with the pistol. Then some posts appeared that mentioned broken Locking Blocks, one of which also mentioned that the pistol shot to one side. And in one post, the Member reported that Glock had replaced a “defective” locking block that was not broken.

Since new, my G34 had always had a loose-fitting Locking Block, Locking Block Pin and Trigger Pin. I noticed that the Locking Block carries an inverted “2” mark on the right side of the frame, as seen in this photo. I will call this a “Type 2 Locking Block”.

Type2LockingBlock_zps773de107.jpg

In my spare parts stock I found an older Locking Block, probably purchased about for years ago, which did not have this mark. I will call this the New Old Stock (NOS) part. I installed the NOS part in the pistol, and it was immediately a much tighter fit.

Taking the pistol to the range to check the sights again, I had to make six right windage adjustments (“clicks”) to center the sight. The rear sight blade is now centered in the sight.

The problem with this pistol shooting to the right was resolved by replacing the loose-fitting Locking Block with one that fit the frame tighter. I took some measurements of the two Locking Blocks, detailed below. I used a small hole gauge and micrometer to measure the Trigger Pin hole in the Locking Blocks, and a caliper to measure the width.

NOS (old style) 1447 Locking Block

Maximum width: .755"

Trigger Pin Holes I.D.: .159", .1595"

Type “2” 1447 Locking Block

Maximum width: .753"

Trigger Pin Holes I.D.: .161", .162"

Old 4368 Trigger Pin, Dull Finish

Trigger Pin O.D. .157”

New 4368 Trigger Pin, Shiny Finish

(Not yet available)

Conclusion

The NOS Locking Block fits the frame of my G34 much more tightly than the Type “2” Locking Block, and both of the steel pins are much more difficult to install with the NOS Locking Block.

The POI problem with my G34 was caused by a combination of the size of the Trigger Pin holes in the Type “2” Locking Block and the loose fit of that Locking Block in the frame.

By changing to the NOS Locking Block, I cured the point of impact problem in my pistol.

Interestingly, there is a new Locking Block Pin, Part Number 4368, described as “Locking Block Pin - fits all except G36 - NOTE: new style pin with shiny coated finish - older pin has dull matte finish”.

Recently I learned that there is a third version of the Locking Block, marked with a “1” on one side of the base and “1447” on the other side of the base. I have no idea how this part measures, or whether it is associated with the windage problem. I will call this a “Type 1 Locking Block”.

Next Steps

I have ordered new 1447 Locking Blocks from Glock to see if they ship the NOS part or a version of the new part, along with new 4368 Locking Block Pins to see if they make any difference in fit of the Type“2” Locking Block.

Summary

My new G34 came out of the box with a serious POI error, shooting to the right. I solved the problem with this particular pistol by changing to a tight-fitting Locking Block.

Watch this thread, once I learn more about the Type 1 Locking Block I will post updates. If you have a Type 1 Locking Block and it’s loose, PM me and we can work a swap, I’d like to have one of those to measure.

I did notify Glock by email about what I’ve found.

Chris

Edited by cohland

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Why don't you just drift the rear sight to the right slightly?

Well, it shot to the right, so the corrections would be to the left, which I made with an adjustable sight, all the way to the stop. Adjusting the sights is one way to cope with the problem of the gun shooting off to one side.

I wanted to solve the problem instead of just coping with it.

Chris

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Fantastic summary of, what seems to be, a periodic problem with Glocks. I own 4 glocks (3 gen 3's and 1 gen 2) and have never experienced this problem (but from other posts it might be that others have). It would definitely be interesting to "hear" what Glock has to say about this.

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I just got a couple of lock block spares. Going to check them tonight. Thanks for the heads up.

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My new G34 came out of the box with a serious POI error, shooting to the right. I solved the problem with this particular pistol by changing to a tight-fitting Locking Block.

This pretty much covers it.

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Fantastic summary of, what seems to be, a periodic problem with Glocks. I own 4 glocks (3 gen 3's and 1 gen 2) and have never experienced this problem (but from other posts it might be that others have). It would definitely be interesting to "hear" what Glock has to say about this.

Probably nothing. My experience with them and problem guns has been that they will fix them, but generally won't say what "the fix" was. Twice, I've sent in pistols that were not functioning reliably/properly (with factory ammo), and both times they came back problem solved, no explanation.

It's interesting that the POI issue was apparently caused by a loose locking block. I would have thought if the locking block was loose in the frame, POI would be erratic rather than consistently off. 4" at 20yds would be about 20MOA, no?

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I believe every Glock I have ever owned, and that is more than a few, has shot to the right. My understanding is that there is flexion in the polymer frame which contributes to the guns needing the sight drifted to the right a fuzz. Whenever I install sights on any glock, I set the rear sight off to the right a hair. All my adjustable sights are set to the right.

Moving the rear sight to the right would compensate/correct for a gun that hits to the left of POA.

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I believe every Glock I have ever owned, and that is more than a few, has shot to the right. My understanding is that there is flexion in the polymer frame which contributes to the guns needing the sight drifted to the right a fuzz. Whenever I install sights on any glock, I set the rear sight off to the right a hair. All my adjustable sights are set to the right.

Moving the rear sight to the right would compensate/correct for a gun that hits to the left of POA.

Your right. I believe the red wine got me last night!

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So, which directions did you really mean?

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I checked the three spare lock blocks I have. #1 had no marking. The other two have the #2 however it is not inverted like yours in the photo. No noticeable difference. Did not shoot them.

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I briefly owned a Gen4 17 that would pattern more than group. I'd been shooting Glocks for about 10 years and was fine with my old Gen3 17. I couldn't figure out what the problem was and dumped it at a loss in frustration.

I wonder now if it was a loose locking block?

(null)

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Good info, I have a relatively new G17 that I had to drift the rear sight about 1mm off the dovetail to get the groups to center. Will check it tonight.

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Where do you get your locking blocks? Do you specify which one you want? I think I may try replacing mine.

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I ended up sending my G17 back to Glock. They called me saying that the slide lock or slide stop was installed incorrectly (don't remember which the guy said, though I cannot think of how the slide stop would be installed incorrectly to affect accuracy...). Gun was brand new with one range trip and 200ish round through it. They said they changed out whichever one was installed incorrectly, and the the locking block, and they sent targets using 124g Blazer at 15 yard that were easily 1.5". Sights were back centered on the slide dovetail. Have not shot it yet, but I hope those targets were what I can expect.

Oh, and they paid for shipping both ways, and had the gun back in less than three weeks. Very good customer service.

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Where do you get your locking blocks? Do you specify which one you want? I think I may try replacing mine.

I ordered then from Glockmeister, hoping that they were the new ones, and they were. I told Glockmeister this whole story before ordering, and the tech I talked with checked the inventory for me to make sure I would be getting the unmarked parts. Could have been just luck, I don't know. Since I'm an Armorer I was also able to order them directly from Glock, and they were all the unmarked parts as well.

Chris

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Did you mess with the new ones yet?

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Did you mess with the new ones yet?

I'm not sure what you mean. I did receive some new Locking Blocks, and when I'm working on a Glock I always check to see if the Locking Block is loose: if it is, I replace it with one of the new ones.

Chris

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I meant if you tried one of the #1 blocks, and how they measure compared to the NOS or the #2 blocks.

I'm wondering if mine isn't more loose than it should be. I need to switch the blocks in my new 17 (#2) with the one in my 34 and try it. The 34 has a lot of rounds through it (I estimate about 6500 at this point). I put the #2 in it but I didn't notice it feeling any different than the other frame. (I would also think the frame would be more responsible for the feeling of how tight the pins are than the locking block itself).

Tonight, I put five rounds on paper to check my new sights on my 34. From 25 yards I had three of the rounds touching, then one about four inches low and right and one four inches low and left.

Edited by AJE

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I meant if you tried one of the #1 blocks, and how they measure compared to the NOS or the #2 blocks.

No, I haven't done anything other than swap out a couple, just wanted to eliminate the POI problem.

I'm wondering if mine isn't more loose than it should be. I need to switch the blocks in my new 17 (#2) with the one in my 34 and try it. The 34 has a lot of rounds through it (I estimate about 6500 at this point). I put the #2 in it but I didn't notice it feeling any different than the other frame. (I would also think the frame would be more responsible for the feeling of how tight the pins are than the locking block itself).

I agree about the tightness of the pins.

Tonight, I put five rounds on paper to check my new sights on my 34. From 25 yards I had three of the rounds touching, then one about four inches low and right and one four inches low and left.

If your G34 (and you) are capable of that kind of accuracy at 25 yards, I'd say you don't have a problem!

Once I swapped out the Locking Block in my G34, I happened to change the sights so I went to the range for some zeroing. Comparing the accuracy of two of my 9mm/147 loads was a real eye-opener, so I'm now using a load that gives me 866 fps and is much more accurate than the previous 950 fps.

Chris

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They were 147gr blue bullets at around 900fps. I was not expecting three of them to be touching.

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My new G34 came out of the box with a serious POI error, shooting to the right. I solved the problem with this particular pistol by changing to a tight-fitting Locking Block.

This pretty much covers it.

So which locking block do i want. Where do i order it from and how do i know it will be the right one, as far as being the tight fitting one? I don't want to order 10 of them just to get 1 tight fitting one. I do have a Glock 17 that has issues...

Edited by bigtimelarry

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My new G34 came out of the box with a serious POI error, shooting to the right. I solved the problem with this particular pistol by changing to a tight-fitting Locking Block.

This pretty much covers it.

So which locking block do i want. Where do i order it from and how do i know it will be the right one, as far as being the tight fitting one? I don't want to order 10 of them just to get 1 tight fitting one. I do have a Glock 17 that has issues...

You know, I find it kind of weird that this is a semi common problem with Glocks. The newer ones are supposed to be MIM and I don't know that much about MIM other than it is supposed to have tight tight tolerances on parts yet the problem seems to be bad locking blocks. Does anyone here with more expertise in this field have an idea of the cause of this issue?

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