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CMC Trigger Review - 3.5 lb Flat Trigger Drop In Unit

Posted by Paul Anderson

CMC Trigger Review - 3.5 lb Flat Trigger Drop In Unit

CMC is a Texas based company with a reputation for manufacturing an innovative, self-contained and easy-to-install AR-15/AR-10 trigger group and I decided to try out the complete experience from door to door on a Patriot Defense 16” Duty rifle, in the Bravo model configuration.

Thanks to the unique design used by CMC, it’s claimed that a match grade trigger pull is now available to anyone and the change out process is straight forward and simple. At first glance, the trigger comes delivered in a package with basic instructions and since the trigger is a self-contained drop in unit, the instructions really don’t need to complex.

I decided to test the flat trigger 3.5 lbs pull weight single stage version as, like most everyone else, curved triggers are currently the standard on all my rifles.

The available CMC models are as follows -

3.5lb - flat (part#: 91503) or curved trigger (part#: 91501)

4.5lb - flat (part#: 92503) or curved trigger (part#: 92501)

5.5lb - flat (part#: 93503) or curved trigger (part#: 93501)

6.5lb - flat (part#: 94503) or curved trigger (part#: 94501)

Unit Description

The trigger type on our test unit was a flat face and it immediately reminded me of the bench rest triggers which look like a straight cylindrical pins hanging down into the trigger guard. Unlike a straight cylindrical pin, the flat trigger has a design that includes a rear web or gusset, which increases the strength and prevents the trigger bending. Not only is the design smart enough to allow for increased strength, the cut out in the web appeals to the eye.

I selected the 3.5 lbs pull weight, since I favour light triggers and I wanted to understand if I could use it in a precision long range AR style rifle also.

The self-contained description is exactly what you get when you open the package. There’s no loose parts or springs to be wrestled, just a single light weight rectangular unit, the two new pins and the torx tools for fitting. No hassle! It doesn’t get any easier than this.

The Change Out Process

For the change out workscope, I opted to complete this myself, since I figured my engineering background would keep me right. As a word of warning, if you don’t have great experience with this type of work, take it to a gunsmith. Other than that, it’s straight forward, just ensure the firearm has the magazine removed and clear the chamber in a recognised manner. Safety first.

I stripped the rifle in the standard manner; Fully unloaded the rifle, removed the pistol grip, removed the safety mechanism and started to drive out the existing trigger pins with a punch. Once the pins where removed, the existing trigger assembly fell out in multiple parts onto the bench. Immediately it becomes clear why a self-contained single unit is a benefit to everyone!

I unpacked the new CMC unit and dropped into the lower assembly. Using the new pins provided by CMC, I gently pushed them through the new unit without any issues and it was a very nice fit. Not too tight, but snug enough to prevent any unwanted movement. The new torx retaining screws fitted on either side of the pins, thus providing anti walk out protection immediately. Even though I own an extensive tool kit, I opted to use the torx keys provided and they made to a similar quality as the trigger unit.

Once the trigger is in place, I re-fitted the safety, cocked the mechanism and gently released the hammer without allowing it to strike the lower assembly. Better to test the mechanism now, before all the other pieces are fitted! I was little intrigued to feel the flat face and it was starting to grow on me.

With a basic function check completed, I re-fitted the spring, detent, pistol grip and added the upper assembly back onto the lower assembly. With the rifle re-assembled, I cycled the charge handle and put the rifle on safe. In the safe position, I tried to release the hammer, without a response. Following this I rotated the safety lever to check that the mechanism had no creep where it could fire upon releasing the safety. No problems so far. Again cycling the action and going back off safe, I gently bounced the buttstock on the carpet repeatedly to induce a hammer drop and as expected, there were no issues with sear engagement. It’s essential in my mind, to test these features anytime you work on or modify a trigger. Also, conduct these prior to heading to the range. While you should never rely on a safety, they provide an additional safety net for unexpected scenarios, especially while hunting or competing.

With safety function check completed satisfactorily, I shouldered the rifle and reached up to feel the trigger for the first time with a correct grip.

Initial Impression

Immediately I noted the Flat trigger gives a point load against round finger tip, rather than a traditional curved trigger bed that covers a large amount of surface area. The flat face gives the impression of an extra sensitivity and this provides more feedback as the trigger weight was taken up.

With the flat trigger sitting further forward than a curved counterpart, the overall finger tip reach is increased around 1/8” which did initially feel a little different. I was really impressed as the pull weight was taken up, the trigger broke clean with no over travel and absolutely no creep. It could be described as much like breaking a piece of pasta. I was sold. I prefer single stage triggers anyway, but this was by far the nicest I had experience to date.

I held the trigger in the rear position, cycled the action again and slowly released it forward as I waited for the reset. With such a short trigger pull, the reset was almost instant and a light audible reset click provide another confirmation. I placed the rifle back on safe again and went through the safety pull test drill one more time. Next stop was live fire at the range.

At the range

For my range test, I decided to use the Patriot Defense Bravo Model 16” Duty Rifle as mentioned earlier and I chose some Hornady 75 gr BTHP Match ammo to match the fast 1:8 twist rate.

This demo rifle is set up where the primary sight system is low mounted Trijicon RMR, and secondary 45 degree back up iron sights down the side.

To start, I picked the 15 yard line for the initial test and used both the primary and secondary sights. With a regular grip, the trigger sits mid way through the trigger guard space, and with a reasonably light pull weight, the rifle performed really well for the initial shots. The use of a reset trigger technique really shows just how well this trigger is made. I delivered a full magazine down range by firing, holding the trigger rearward then gently allowing the trigger to reset and firing again. It’s a smooth pull and the flat face, as expected, gives a controllable response. The absence of any creep whatsoever builds confidence quickly. For the second magazine of ammo, I opted to roll the rifle over and use the 45 degree iron sights. This changes the grip position and between shots I started to work the safety with my trigger finger, just for convenience. Getting back on the flat trigger felt better than a curved, as I could feel the point load immediately. No problems for close in work.

Next, I opted to move over to the 200 yard firing line with primary RMR sight and shoot at some small patches of grass on the back stop berm. Rather than sit down at the bench, I sat on the ground between the benches while resting my elbows on the inside of my knees for better control. Again, I was pleasantly surprised with the short trigger travel which allowed for more control. Having shot in long range competitions for a few years and as an engineer, I loathe vague triggers with any hint over travel or creep. I guess everyone does, but for me I can see the mechanism working as I pull the trigger and this CMC trigger made me smile.


The application of this trigger in a 16” CQB rifle is obvious, but I could easily see this being used in a short to medium range precision gun. The flat trigger gives the impression of a much lower pull weight, but the crisp break point makes all the difference. Being drop in unit, anyone can fit with relative ease. The other big benefit is cleaning. Being able to remove the unit and clean with a solvent, blow dry with canned compressed air and re-install would take minutes. Very handy when you are outside of the house.

Downsides?? Not sure there are any. It’s a quality product at a reasonable price and the upgrade process is easy, making it within reach of most everyone. Just remember the pull weight is not adjustable, so if you buy it for a specific task and find it too heavy then you are stuck with it.