What To Do If Your Polymer80 or Glock Double Fires? It May Be Your Aftermarket Connector

A problem that can happen with a Glock-type of pistol is known as “doubling” wherein the pistol fires one round when the trigger is pulled and a second one when the trigger is released. For those of you all excited about learning how to build a binary trigger for a Polymer80 or Glock pistol, this is not the way to do it. The problem almost always happens when someone starts adding modified components vs. OEM Glock or goes polishing/sanding on parts.

Modifications to the fire control group can lead to unpredictable results because of stacked variation – this means that each little part can vary a little and when you add them all up, you can wind up with way more than the acceptable level at the end. With this in mind, you always want to test functionality before going to the range the first time and when you fire for the first time, load one round. The next time load two and remember to keep the pistol safely pointed downrange at all times.

I bet the pistol has been modified for this to happen

Okay, for a Glock design to double, somebody has altered the geometry of some of the parts through polishing or maybe they swapped parts, went to aftermarket parts, bent something, sanded on something, changed out springs that cause the firing pin lug to jump the sear — bottom line, something was changed. If you went with aftermarket parts, sanded or polished some of the fire control group and are now trying to figure out what happened, I’d recommend you replace whatever you touched with OEM Glock while you figure out next steps.

Today’s story focuses on the role of the connector

Well, Gaston Glock was a firearms genius and designed a unique fire control group (the trigger, firing pin, connector and what have you) that was unique at the time. One could argue a lot of companies have copied his design pretty closely.

Glock wanted both a reliable and safe pistol and the interesting thing was that he had no prior firearms design experience before the original Glock 17. Probably in part due to this, he came at the problem with an original point of view and created his “Safe Action System”.

What we want to focus on today is the connector. The connector is a metal stamping at the rear of the pistol connected to the trigger housing. When the trigger is squeezed, the connector forms a ramp that guides the trigger bar downwards thus releasing the firing pin. When the slide returns, the hook on the connector follows the track in the slide and the connector should move to the side allowing the trigger to reset . When the trigger is released it moves back into position for the next cycle. If the geometry is wrong for whatever reason, it will fail to block the firing pin from returning forward resulting in doubling.

The angled piece of sheet metal is the connector.
This gives you an approximate idea of where the trigger bar engages the ramp that the connector forms.

Let’s Watch A Video

To be honest, I feel like every time I watch a video or read something about the Glock design I learn more and sure don’t claim to be a Glock guru. I sure am a very interested user of the design though I prefer Polymer80 frames and their angle to an actual Glock brand pistol.

Watch this excellent animation on how a Glock works and pay attention to what the connector is supposed to do – this is what can go wrong with an aftermarket connector.

My Doubling Story

I took my brand new Polymer80 build G34 pistol to the range for testing and, hopefully some fun. A model 34 is basically a model 17 with a longer barrel and slide. My intent with it was to be a range gun so I tricked out just about everything. I literally think the magazine release spring, trigger block and extractor were the only OEM parts 🙂

When I took the pistol to the range and started test firing it was immediately apparent there was a problem because the pistol fired on the pull and release. It was inconsistent as well sometimes firing just one round and sometimes firing on the pull and the release. I was bumming because I meant to pack parts with me if I had a problem and forgot so it went back in the case while we tested other firearms.

So, what happened?

After I got home and started working on it, I realized I really hadn’t function tested it repeatedly enough. I definitely paid very close attention to what the pistol did when I released the trigger after racking the slide. I could replicate the doubling most of the time just like what happened at the range – it wasn’t doubling consistently during testing either, which is why I missed it.

Function testing going forward

Based on what I learned, here’s what I would recommend for function testing and do it 3-5 times before you go to the range:

  1. Absolutely make sure the pistol is clear / unloaded – both the chamber and the magazine.
  2. Squeeze the trigger just to make sure you are starting with an uncocked pistol.
  3. Rack the slide
  4. Pull the trigger – you should hear a click. DO NOT LET GO OF THE TRIGGER – Keep it pulled back.
  5. Rack the slide again with the trigger pulled
  6. Now listen carefully and watch the slide, when you get go of the trigger do you hear a click as the firing pin incorrectly goes forward? If so, you have a doubling problem.
  7. If you did not hear a click, go ahead and squeeze the trigger as you normally would and you should here the click of the firing pin.
  8. Now repeat steps 3-7 and pay attention when the slide cycles with the trigger being pulled. It should never fire upon release.

I had researched the springs and trigger carefully. What I questioned was the connector and it did turn out to be the Apex brand connector. To address the problem, I replaced it with a standard OEM Glock connector – problem solved. Note, this can happen with other aftermarket connectors as well such as Ghost so I am not singling out Apex. There’s no way a manufacturer can take all the possible combinations/variations into account so I don’t blame them at all – it simply happens and is something you should not be surprised about.

The top is the Apex connector and bottom is the OEM Glock connector that I installed. It’s interesting to see the slight shape differences in the angled surface that guides the trigger bar down.
There’s a trick you can sometimes do to swap connectors – not always but sometimes. This is the G34 that had the problem. First, press out the pin that holds the trigger block in place. By the way, ignore the Glost packaging to the left. I was looking at it and am too lazy to take another photo right now while I am writing this post 🙂
Sometimes you can gently lift the block out far enough to get a fingernail (or whatever) under the connector, lift it out of the block and then press the replacement in. That’s what I did here. I then reinstalled the block, its pin and function tested the pistol. It passed with flying colors after the swap.

A more thorough video on changing the connector from the folks at Brownells

In Conclusion

If I have time in the future, I may contact Apex and see what they recommend I do but for now, I’ll stick with the Glock connector. One of the key takeaways I want you to have is that it is important that you test your builds before you ever rely on them. If it fails, ask yourself – what did I just change and focus your efforts there.

Click here if you want to see other posts about Polymer80 pistols.

I hope this post helps you out.


Polymer80 and Glock Parts Vendors

When you want to customize your Polymer80 or Glock, or you need replacement parts, there are a number of solid vendors you can go to:

Those are all reputable vendors and aren’t going to sell you inferior counterfeit products.


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