Shooting Skills: AR15 Trigger Choice, Continued…

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Improving an AR15 trigger ranges from total redesigns to minor changes, and here are a few not to overlook.


Glen Zediker


Last time I used all the space I had talking about the two essential AR15 aftermarket styles, single-stage and two-stage. There was more to say, and here that goes:

Modular triggers
Most two-stage and single-stage triggers work off the existing AR15 trigger architecture, but there are those that don’t. Some are self-contained and self-defined. These “modular” triggers are all way on better than stock, to be sure. What they are, are complete housings that contain the hammer and trigger captive within the housing, installed, tuned, and adjusted as a unit (some are user-adjustable, some are not). They “drop in” and the housing is then secured by the original pins. The pins, however, don’t function within the trigger unit itself.

Timney
This is a Timney modular-style AR15 trigger. Take out the old trigger, drop this one in the lower, secure the stock pins through the holes in the Timney housing (and make an adjustment to secure the housing against the lower receiver floor). Done. All the modular-types I’ve tried are better than stock, indeed. I can’t warrant durability though, because a few out there look a tad amount spindly. This one has been reliable so far.

A modular trigger is about the easiest way to a better trigger. The question with the modulars is how well they hold up, how reliable they will be. There’s a difference in the natures, and outcomes, of stress-in-use comparing target shooting and varminting to the pounding a carbine might get in a 1000-round range session. I have not put a huge number of rounds through any of the modular units and, therefore, have no notebook references. I do, however, know a good many others who have and whose opinions I value. Consensus is that not all are 100-percent.

Pins
Many aftermarket triggers come with a set of proprietary pins, and if one does, use them. If not, a better pin set can make a difference in trigger performance.

KNS AR15 trigger pins
Here’s a standard-form pin set from KNS. They’re correctly and consistently sized and dead straight. Trigger pins and hammer pins are the same, but they don’t function in the same. Each pin is installed from the right side of the receiver, un-grooved end first, and pushed through to the left side of the receiver. The grooves function to engage the trigger return and hammer springs, preventing the pins from out and out coming out of the rifle. Install from the right side of the lower receiver, pushing it through to the left side, ungrooved end goes first. Lube the pins!

Look at how the system operates and it’s clear that pin straightness and circumference influence trigger break and function. The pins in the standard system are also free to rotate. If the pin is a little undersized or a little bent, or both, that means engagement won’t be consistently the same each time.

And sometimes it’s not all the fault of the pins. The receiver holes also have to be what they should be. I’ve had fit mismatches from time to time, and the way to fix it is usually in the pins, because they are usually a tad amount too small. However! It’s not always a straight-up fix to purchase “oversized” pins.

One (strong) caution if you opt for “oversized” pins: make daggone sure prior to installation that the trigger parts are fully free to move as they should on the pins. The hammer, especially, should have zero drag. Sometimes a little very careful polishing on the center point area of the pin is necessary to attain a “perfect” match.

Oversized AR15 trigger pin
Here’s an oversized pin. Check diameters with a micrometer and compare them to blueprints. Standard should be 0.1540 inches (+/- 0.0005). Oversized usually adds 0.0010. Also! Check the receiver holes. Easiest to do with a #23 machinist’s drill bit (use the butt end of it); that’s a 0.154 size (get a 0.155 also, if you can find one). Make the right match! Don’t pound an oversized pin into a smaller-size receiver hole! If you do then you’ll get into a cycle… For conflicting circumstances, KNS offers a well-oversized pin packaged with a reamer to suit. Best proceed with care, though.

To preclude pin rotation, a “locking” pin set is the trick. Even oversized pins can move. There are a few different takes on lockers, and I put a set on all my race guns.

Better pins can also make a positive difference in modular trigger installation.

KNS locking AR15 pins
Here’s a set of KNS locking pins. There are different styles, and all function to fix the hammer and trigger pins against any movement, providing an unchanging base for a match-quality trigger.

Springs
Another simple trick I do, when I can, is install a pair of chrome-silicon trigger return and hammer springs. This material is radically superior to the standard music wire used otherwise. It rebounds faster at a lighter “weight” than a music-wire-based spring. That means easier operation with no sacrifice in tension. Chrome-silicon also lasts the life of a rifle. All music wire springs will break down and lose power, so simple replacement of the hammer spring every 2500 rounds or so can be a maintenance routine item to maintain peak performance. Trigger return springs, no so much. They’re not under much stress.

A chrome-silicon replacement set will reduce trigger pull effort a tad in a stock setup, but unfortunately won’t do a thing to improve its movement quality.

An extra-power hammer spring is a commonly-used addition to a competition gun, and the reason is pretty much to reduce hammer fall time. It works. However, be warned that an extra-heavy spring can wear the receiver holes; after some time, the holes can get a little oblong and, along with it, larger. If you want to run a heavy spring, get a very well matched fit prior to installation of the spring. This stays off hole wear because there’s just no room for movement.

CS AR15 trigger and hammer springs
A chrome-silicon spring pair will improve trigger pull some, but mostly these springs last for a good long while. They just don’t change over 100,000+ cycles. Chrome-silicon has better rebound behavior so the hammer hits a little quicker. I use them in any trigger where they’ll fit. These are manufactured by David Tubb, Superior Shooting Systems.

Lube the fool out of the trigger! Simple as it may seem, keeping the works slicked up goes a long way toward making a trigger feel better and last longer. By “last longer” I mean retain consistent feel and weight. This is especially important in a two-stage. It can’t be over-lubricated. I use light grease with boron-nitride for the engagement surfaces and hammer face (bolt carrier slides across this) and oil for the rest of it.

The only exception is for those who are out in the field in sandy and dusty conditions, or in extreme cold, and then I’d suggest one of the “dry” lubes. But some lube always!

AR10
If you have one of these, make double-dang certain your new trigger is performing correctly. The AR-10/SR-25 types are beastly in cycling. When that honking bolt carrier slams back home after chambering a round, the inertia residing therein can trip a lot of the aftermarket triggers. It’s a shock. What happens is the disconnector, well, disconnects and loses its previously captive hammer. Especially some of the modular units just won’t function safely on a big-chassis rifle.

The preceding was a specially-adapted excerpt from the book The Competitive AR15: ultimate technical guide by Glen Zediker and Zediker Publishing available from Midsouth Shooters Supply.

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