Gun-ology: Debugging a Gun (Glock)

“Gun-ology” is our general gunsmithing series.  In this series, we strive to provide you with information for basic to advanced gunsmithing skills, as well as valuable and current gun knowledge.

In this “Gun-ology” article, we present a case study of how we “de-bugged” an issue with the trigger function on a Glock G35. Also, we identify a scenario with Glock upgrades that may save you time in your own gunsmithing/shooting.


Previous to this issue, we performed a trigger upgrade to a Glock G35 several months ago.  This trigger upgrade consisted of replacing the OEM connector, the OEM trigger spring, the OEM striker spring and the OEM safety plunger spring. The replacement parts consisted of using a Ghost Edge trigger connector and the Ghost complete spring kit. There is a 4 and 6 lb selection in the striker spring assortment – I used the 4lb spring.

During a recent training session, my fiber optic sight came loose on my Gen 3 Glock and I had to use my Gen 4 to complete the coaching session (I am currently shooting my Gen 3, while using my Gen 4 as a back-up at the moment).  The first thing I noticed was the trigger was breaking with extremely light pressure (sub 2 lb) and was causing me discharges when I was not on target. Secondly, I noticed that the mechanical trigger safety was periodically catching, at first, I thought it was my finger placement. I noticed, after a few iterations, without changing my finger position on the trigger, the safety seemed to catch and block my trigger movement.

Very frustrating!!

I initially had a feeling that it was the stock trigger safety that was defective, so I called Glock. They responded that I would have to send the gun back to them for inspection and/or repair and that it could take anywhere from 8 to 12 weeks to complete and it had better have all of the stock/OEM parts installed!

An aside, if you ever DIY on a gun and you are not one of their (Glock) certified armorers, then you had better not send them a gun that is not completely installed with OEM parts! If you do, you may get charged for their “work” of reinstallation and you may not get your upgraded parts returned back to you!

An additional aside… When you DIY, keep those OEM parts!

Since I had to replace the OEM parts anyway, I decided to try a few things. My initial goal was to resolve the ultra-light trigger break – as I made some changes I thought I noticed the trigger safety issue disappearing!

So, I decided to de-bug this gun myself (Note:  thank you Glock for making me do this!).


Here is the basic procedure you should follow in order to de-bug a gun:

  1. Define a singular and specific issue – In this case, my issue was that the trigger safety was randomly catching.
  2. Define a reproducible test scenario for the issue – In this case, I identified that I could not pull the trigger 5 times straight without the safety catching. (Note: if you can not define a reproducible test scenario. then you have not isolated the problem and you should NOT proceed).
  3. Return the gun to ground zero – This means to undo ALL of the changes you have made to the gun and replace any replacement/upgraded parts back with the OEM parts. I will emphasize again… undo ALL of the changes made to the gun. Even if you can not imagine how a change would make an issue occur, still undo it. Trust me, in this case, I never considered that this change would have produced the issue that I was having.
  4. Verify that the condition DOES NOT exist in the “ground zero” state – Run the test scenario you have identified and verify that the issue does not exist in the original “ground zero” state. If you find that it does exist in the ground zero state, then you may have an actual defect with the gun. If you are not an advanced gunsmith, this may be the point where you take the gun back for warranty repairs. Personally, this is where I would put the gun in my “O.K. to MacGyver on” pile and start destructively de-bugging (I will present this in a later article).
  5. One part at a time, change out the OEM parts, reassemble gun and run test scenario – Do one part change at a time, swap it out and then re-test. In this step, you are attempting to isolate the change that is producing the issue. Return the OEM part after testing and before you change it out with another part. This is  a “one change” testing. Generally, at this step you will find the one part that is the cause or shows to be the origination of the issue.
  6. IFF (if and only if) the “one change” testing does not reproduce the issue, then do two changes at a time and re-test – Now, you are doing a “cross change” testing. Oftentimes, particularly with tight tolerance guns like Glocks, an issue is caused by tolerances stacking due to multiple part interactions.

From step 6 in this procedure, continue with 3-component change testings until you find the “X” change that produced the issue.

Normally, the first change testing will identify the “suspect” part/problem.

Once you do identify the problem, resolving it then becomes a choice: a) replace the “suspect” parts back to the OEM parts or b) do some research and see if there are other equivalent non-OEM parts available.

Case Study

My Glock G35 trigger safety was inappropriately sticking and blocking the trigger during normal functioning (the issue). I determined that if I “functioned” the gun 10 times consecutively, I could produce this issue one or more times (the test scenario). My suspicion was that the trigger safety was defective (this is your hypothesis, but can also become your bias if you are not cautious).

After replacing all the of the OEM parts back into the gun (yes, I had kept them – woo hoo!), I “tested out” my test scenario. The issue did not occur in over 30 test attempts (Note: I went beyond the believed test scenarios – this is always a good idea). At this point, my hypothesis (a defective OEM trigger safety) is proven to be incorrect and now is a bias I must be careful about in further testing. If replacing all of the OEM parts eliminated the issue, then the issue is not a defective trigger safety.

Be careful about hypotheses/biases – they can lead you on wild goose chases!

Next, I proceeded to replace one part and re-test, this time replacing the connector and then re-test this change – still, I could not reproduce the issue. Then, I replaced the trigger spring and re-tested – still, I could not reproduce the issue. On the third change, I replaced the striker spring and re-tested – low-and-behold, the ISSUE!

I was in disbelief! How could the striker spring cause this issue? I immediately put the OEM spring back in and re-tested – no issue. I put the Ghost spring in and re-tested – issue. I was actually in such disbelief, that I performed this 4 more times just to make sure (I am a bit hard-headed like that).

The 4lb Ghost striker spring was causing the issue!

At this point (if you are not me), you can just decide to use the OEM spring (as I did) or try another vendors’ spring (which I also plan on doing at a later time). For me, though, I needed to understand the “why” of the issue.

Glock Issue

After a lot of back and forth swapping out of parts, testing and trying AND looking at the gun under 3x magnification to see exactly how the parts were moving and functioning, I can tell you what I believe was the fundamental issue.

With the 4lb striker spring, as pressure is taken off the trigger, the trigger was not moving fully (I would say firmly) forward – I would deem it as “limp trigger reset”. For whatever reason, this occasionally caused the trigger safety to flex (left/right) in the slot at the trigger causing the edge of the trigger (regardless of being engaged or disengaged) to catch. Now, this may still be a defective trigger safety or an over-cut trigger safety slot, but replacing the striker spring to the OEM clearly resolved the issue. Since doing so, not once has the problem reoccurred.


De-bugging gun issues can be done by anyone, and it does not necessarily require having gunsmithing skills. We have provided a procedure to follow that can help you determine and resolve your gun issues. Also, we have identified a Glock compatibility issue that we hope may save you time and energy in your own Glock usage. If you own a Glock G35 (or possibly 34) or a Gen 4 and you find that your trigger safety catches, change out your striker spring and see if the issue is resolved.

Leave a Reply