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Trigger Pin Bushing: Makin' it pull straight through!

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One of the things that has always been a nagging annoyance to me with respect to the Glock trigger is the tendency for the stock trigger to deflect laterally when the pulling force isn't applied directly rearward.  Frankly, the Glock trigger simply wiggles.  Lateral movement in the trigger is bad for repeatability/consistency in your trigger pull motion.  This applies whether you're running through an IPSC or IDPA stage, target shooting, or (heaven forbid) using your weapon for self defense.

The main reason for this is that the trigger pin to trigger pin through-hole clearance is too large.  I discovered this back when I owned a Glock 22, but the lateral play is evident in all models.  I've come up with a fix.  I designed a special trigger pin bushing that, when installed and tuned properly, eliminates virtually 100% of the lateral play in the trigger.  Here's an image of the bushing installed on my Glock 35 trigger bar.

Click for larger version...

Before installing the bushing, the lateral play in my trigger was in excess of 0.004" (limited by the trigger opening in the frame).  Doesn't sound like a lot, but it is.  Compare a 0.004" lateral play in the Glock to a zero/near zero deflection in a 1911/2011 (STI, SV, et al.).

Notice what I placed in parentheses above, "limited by the trigger opening in the frame".  IF the frame opening were larger, the deflection would be even greater.  But worse, that "limiting" is actually adding drag to the pull through via the trigger dragging on the frame opening!  Drag mean a larger pull weight, and it's NOT always consistent.  The more lateral load you apply to the trigger, the greater the drag, resulting in a less than repeatable trigger pull weight in actual use.

A lesser, but measurable, additional problem with the large clearance is that the trigger and trigger bar can actually displace vertically during the pull.  Now, on a stock trigger, this might not seem like such a big deal, but if you've tuned your trigger bar to connector junction to get a lighter/smoother trigger, the vertical displacement changes the point at which the two parts contact.

The bushing is machined from an oil-impregnated bronze material.  As machined, the bushing has an undersized inside diameter and is oversized in length.  I had a custom reamer made to match the inside diameter to the outside diameter of a POLISHED trigger pin.  The clearance is set to something on the order of 0.001" max.  Actually, it is something less than this.  Once the reaming is completed, the bushing is lapped to the trigger pin with non-imbedding, ultra-fine lapping compound.  The abrasives in the compound are broken down by the lapping process.  The result is a very smooth and consistent match between the bushing and trigger pin.

The bushing is pressed into the trigger.  The trigger is jigged into the drilling machine.  First, the existing through-hole is enlarged with a carbide drill bit to facilitate entry of a reamer. Then a second custom reamer is run through the trigger to set the through-hole diameter for an interference fit for the bushing.  The reamer size was chosen to 1) offer a permanent interference fit, and 2) such that it would not over-stress the polymer material in the trigger.  Then, without removing the trigger from the jig, the bushing is pressed into the trigger with another tool fixed in the machine.  The drilling machine is used as the arbor because 1) it doesn't take a great deal of force to press the bushing, and 2) it minimizes the chance of misalignment between the bushing and the trigger.  Finally, the machine can be indexed to set the bushing's lateral position within the trigger to locate the trigger in the frame opening.


With a nominal 0.001" clearance distributed over the longer nominal length of the bushing, the maximum deflection is less than 0.017 degrees. The stock deflection is on the order of 0.742 degrees. That's a 97.79% reduction in lateral AND vertical deflection of the trigger to trigger pin.  It'd be great if that was all there was to it, but it gets better.

With the bushing installed, we can locate the trigger within the frame opening to eliminate/minimize any trigger contact with (and hence drag on) the frame opening.  This significantly improves the pull consistency from cycle to cycle.

Additionally, (and I'm still analyzing the "Why?") on my Glock 35,  installation of the bushing has significantly reduced deflection in the trigger bar arm in its path around the magazine.  In fact, setting the trigger centrally in the frame opening, has actually eliminated the contact I used to have between the trigger bar span and the frame adjacent to the mag well.  My supposition at this point is that reducing the lateral deflection in the trigger also reduces the lateral deflection in the trigger bar pin since they are both located in the same vertical plane.  I would assume that this is also making the trigger bar to connector interface more consistent.  I will have to do a wear pattern test to verify this however.

Some other tips/tricks/lessons learned:

1) The slide stop lever's through-hole for the trigger pin is a punched hole and thus is deformed.  It's important to lap the sides of the slide stop lever smooth to maximize the  bearing surface. Polish the mating surfaces after they are flat.

2) The slide stop lever spring is more than likely NOT properly aligned.  (See my other article).  It's important to align the spring properly before installation, and then make sure the spring tip is slid over against the frame under the upper locking block pin (if any).  One alternative to make sure this is the case is to machine a shallow groove in the locking block pin in the appropriate place to insure that the slide stop lever spring stays properly located.  However, doing this will require you to depress the spring slightly when removing the pin to prevent spring deformation.

3) Polish the inside surfaces of the locking block legs where the trigger pin penetrate it on both sides.

4) Set the bushing length to a dimension just slightly less than (the distance between the locking block legs MINUS the width of the lapped flat slide stop lever). This will minimize/reduce the rotational friction between the bushing, the right locking block leg, and the inside face of the slide stop lever.

5) When you install the trigger pin, feel for the click as the slide stop lever drops into the groove, and then push the pin until the slide stop lever is pinned against the left side of the frame.  if you do this AND set a 0.001" clearance between the left side of the bushing and the right face of the slide stop lever, you will have minimum rotational friction AND maximize the locational and deflection reduction effects of the bushing.

That's all for now...  I will expand on this article with more details, images, and How-To's as time permits!

Click for larger version...






Copyright (C)2003 MONTAC Enterprises.  All Rights Reserved©
Revised: March 03, 2006 .