Glock Optics Installation: Don't Let One Small Screw Ruin Your Build
So you finally pulled the trigger (pun intended) on a red dot for your Glock. You've got your optic, and a fistful of screws — and you're ready to get to work. But before you start torquing things down, there's one gotcha that catches even experienced builders off guard: the right-side mounting screw.
A Little Background
Modern Glocks (particularly Gen 1-3 models) have become a popular platform for red dot optics. This is a simple modification that can cause a surprising amount of headache if you aren't aware of this very niche issue. This extractor issue is only relavent on direct mounted optics.
So if you're running a an optic with an adapter plate then you can ignore this.
If you are still looking for a slide or shopping for a new one check out our wide selection of Glock compatible slides
The Problem: Right-Side Screw vs. The Extractor
Here's the issue: the mounting hole on the right side of the slide sits in very close proximity to the extractor channel. The extractor is a spring-loaded component that grabs the rim of a cartridge as it feeds into and removes the cartridge from the chamber. It's a critical piece of the reliability puzzle.
When you install your optic, the right-side screw threads down into the slide — and depending on the screw length, it can protrude just far enough into the extractor channel to bind, drag, or interfere with the extractor's movement. The result? Failure to eject (stovepipes), sluggish extraction, or or other issues in the extraction phase of the cycle.
The frustrating part is that the gun may look perfectly fine from the outside. The optic sits flush, nothing seems obviously wrong — and then you hit the range and wonder why your previously reliable Glock is suddenly choking.
Why This Happens
Most optic mounting kits ship with a one-size-fits-all set of screws. The problem is that "fits all" rarely means "fits perfectly." The geometry of the Glock slide means that the left-side and right-side mounting holes are not always equal in terms of how much screw depth is safe. The left side generally has more clearance, while the right side — sitting closer to the extractor — has a tighter tolerance.
Some quality aftermarket mounting kits account for this by including screws of slightly different lengths — a shorter one specifically intended for the right side. If your kit came with two screws of clearly different lengths, that's intentional. Use the shorter one on the right. Don't mix them up.
However, many kits — especially budget options — ship with matched screws of the same length, leaving it up to the user to sort out any interference.
How to Check for Interference
Before you ever load a live round, do a functional check (best to use dry fire rounds or blanks):
- Snug the screws down (don't fully torque yet).
- Manually cycle the extractor by pressing on it from the breech face side with a punch or the tip of a pen. It should move freely and spring back with authority.
- Listen and feel for any dragging or stiffness. A healthy extractor snaps back crisply. If it feels sluggish or gritty, back the right-side screw out a quarter turn at a time and recheck.
- Remove the barrel and look into the extractor channel with a light. In some cases, you can actually see the tip of the screw intruding into the channel.
The Fix: Shorter Screw or File It Down
You have two main options:
Option 1: Source a Shorter Screw
The screws used in most Glock optic mounts are typically M4 or 6-32 thread, depending on the plate manufacturer — always check your kit's specs. Finding a screw that is 1–2mm shorter than the stock right-side screw is usually all it takes to clear the extractor without sacrificing thread engagement. Hardware stores, specialty fastener suppliers, and optics manufacturers' customer service lines are all good sources. The screw overall length (including the head) should be about .4 inches long or 7/16ths
Aim for enough thread engagement to hold the plate securely (generally at least 2–3 full thread depths into the slide), but short enough that the tip doesn't reach the extractor channel.
Option 2: File or Grind the Existing Screw
If sourcing a new screw isn't convenient, you can carefully shorten the existing right-side screw yourself:
- Chuck the screw into a drill or hold it securely in a vise.
- Use a fine metal file or bench grinder to remove material from the tip — go slowly, removing a little at a time.
- Deburr the tip when done so it threads cleanly without chewing up the hole.
- Reinstall and re-check extractor function after each small reduction.
Take your time. You can always remove more material, but you can't put it back.
Torque and Thread Locker
Once you've confirmed the screw length is correct and the extractor moves freely:
- Apply a small drop of medium-strength thread locker (Blue Loctite 242 is a popular choice) to each screw.
- Torque to the optic manufacturer's specification — typically around 15–18 in-lbs for most red dots, but always defer to your specific optic's documentation.
- Allow the thread locker to cure fully before heading to the range.
Final Thoughts
Mounting an optic on a Glock is one of the most rewarding upgrades you can make — a quality red dot dramatically improves target acquisition and makes the gun genuinely easier to shoot well. But like any build, the details matter. A screw that's a millimeter too long can turn a perfectly reliable pistol into a jam-o-matic.
Take the extra five minutes to check extractor function before you head to the range. Your future self — the one not clearing malfunctions under the hot sun at the 25-yard line — will thank you.
As always, consult a qualified gunsmith. A quick bench visit is far cheaper than diagnosing reliability issues the hard way.
