Product Design


The module box that contains the CMC trigger group is designed to keep side to side wall thickness as close to standard as possible. This means that if buildups of grease, grime, sand, powder residue, etc. occur, the internal parts still have the clearance to continue to function as the factory standard designs would function under these conditions. Had the internal geometry been closed in around the moving parts to center and/or contain the internal parts, it wouldn't take much to contaminate the parts, lose clearances and result in malfunctions. The stainless steel, sheet metal module is a very high-tech, close-tolerance, and critical component with +/- .001" tolerances in areas critical to function. A very high quality component that is not easy or cheap to make.


No matter what methods are used to secure them, screws can and will come loose and we have done everything possible to avoid Murphy's laws

And we all know that when Murphy's laws strike, they will normally occur at the worst possible times. Using screws to attach the trigger module to the receiver, would not only offer no benefit, but it would also be very counterproductive to the design objectives. Nor would screws secured with adhesives add to the effectiveness of the mechanism. The CMC design purposely does not rely on any screws or adhesives that could in any way allow some part to loosen and cause a failure.


If some well-meaning, unqualified human can tamper with a perfectly functioning mechanism, they will. We feel that we can't allow that, for people who put a premium on reliability and the huge majority who understand the disadvantages, wouldn't tolerate it anyway.

Adjustability means an additional part or parts would have to move in addition to the components that absolutely must have movement. Clearly, adjustable features would offer no benefit to reliability, but could definitely compromise reliability. Furthermore, do to the nature of the design, adjustability is not necessary.

Why is adjustability not necessary? The only valid reason we can see that adjustability would serve any purpose toward reliability in an AR-15 rifle, would be to ease and reduce the time during the installation of the old style trigger groups, where you begin with a bunch of loose parts. You see, the fact is, every different brand of AR-15 rifle receiver is more than likely built to a different set of nominal dimensions and tolerances, even when based on military specifications. To add to the problem, many AR-15 rifles are reverse engineered without any reference to the military prints. To make a precision set of individual parts to one recipe (the same geometry for every respective part) that would function reliably in every different brand of AR-15, is clearly and obviously unlikely. This is surely why we don't see a complete set of individual parts that will drop-in, without any fitting required, offered for sale.

So if you ignore the reliability factor and Murphy's laws, adjustability in a loose set of trigger group parts might be useful. But obviously, to maximize reliability it's best to have a set of non-adjustable trigger group parts installed by a qualified, experienced gunsmith who can fit, file, hone, check for safe and proper function, and then keep that group of trigger parts dedicated to the rifle they were fit to, exclusively.


With the CMC drop-in AR-15 trigger you are buying consistency that narrows the only remaining proficient gunsmithing questions down to what AR-15 gunsmith is qualified to insert two pins and proficiently determine the results have yielded safe and proper function.

If you want to take any given trigger module out of one rifle and move it into another, and then again to another rifle, and so on, the same level of AR-15 gunsmithing proficiency applies; who can proficiently insert two pins and determine the results have yielded safe and proper function? The lower receiver has to be pretty far outside of the military specification geometry for the CMC drop-in AR-15 trigger module not to fit and/or yield safe and proper function.


We believe the necessary elements to match precise trigger control with a fire control system that will dependably function up to the highest standards are experience, knowledge, state-of-the-art design, testing, very close tolerances, precision manufacturing and quality control.

After years of producing and improving processes, and geometry; the newest generation of CMC drop-in AR-15 trigger modules have brought every element of what yields Tactical Grade quality, up to the most demanding levels.


A clean, crisp trigger release and 3.5 pound nominal pull weight. Key elements to any trigger group that allows the shooter's performance to meet the potential of the firearms.

CMC's drop-in AR-15 trigger modules are factory set to a nominal trigger pull weight of 3.5 pounds. To most people, a truly clean, crisp breaking trigger pull set at 3.5 lbs. seems much lighter. If you know anything about the outstanding marksmanship demonstrated at the Camp Perry Championships by shooters using a minimum 4.5 lb. trigger then you will not have any doubts about what is possible with a 3.5 lb trigger pull.


These elements are critical to the overall performance of a world class shooter, but are also important to any shooter who wants to demonstrate precision shooting.

Unlike traditional AR-15 trigger groups, one of the most spectacular elements of the CMC AR-15 drop-in trigger modules is that tactical grade over-travel and take-up can be accomplished with geometry and without the need for screws or other moving parts. Sure, some people have different preferences, but due to the many years CMC's trigger modules have been in production and the many thousands sold, customer feedback has made us very confident that the design of these products is such that take-up and over-travel is right in the sweet spot for both. And it won't change because it's done with geometry on not moving parts that can come loose (usually at the worst time).

1. Every component of the CMC drop-in trigger modules maintain tolerances of +/- .001" (one thousandth of an inch) or less wherever two critical surfaces engage or interface. The same tolerances apply to each and every hole location.

2. Surface finish is critical for obtaining that magic "feel" that is absolutely necessary with a tactical grade Quality trigger group. It's not easy and takes of a lot of time to develop an effective, precision tooling setup for producing mirror finishes on the components with critical surfaces as are incorporated in the CMC trigger modules.


How important is reliability to you? CMC's drop-in AR-15 trigger modules get their outstanding combat reliability and service life, and tactical grade quality & trigger pull without compromises like reduced sear/hammer engagement or using reduced power springs.

The cheap, easy ways to reduce trigger pull weights are by minimal sear/hammer engagement and reducing spring rates on the trigger return spring, and the hammer spring. But CMC's way of thinking is that the cheap, easy methods are very counterproductive to the objectives for this design. For one, reduced spring forces increase lock time (the time from when the trigger releases the hammer until the hammer strikes the firing pin) which reduces accuracy potential. Second, reduced spring forces can cause trigger groups to fail much easier in grimy, dusty and/or fouled conditions. Third, reduced spring force on the hammer causes light strikes of the firing pin on the cartridge primer. The potential for light strikes has two problems that are especially concerning in AR-15s; failure to discharge the round is the obvious problem, but also, if the rifle is fired a lot without cleaning (especially in nasty environments) fouling can cause light strikes to occur long before they would have with full power springs. Also, for those of us that like to go to the range and practice or shoot a lot, it's nice to be able to reliably use inexpensive military surplus ammunition, which can be done with the CMC trigger groups. However, for those of us that also like to do serious precision shooting with high quality ammunition, it's nice to know that you have a great tactical grade trigger pull that facilitates precision with very fast lock time. What are the benefits of settling for less?

Engagement – The amount of engage of the sear tip to the hammer cock notch is extremely critical for reliable function under varying conditions. The cheap and easy way to obtain reduced trigger pull weights is by reducing engagement to bare minimums. Maybe that's OK for bench rest rifles, match only rifles or rifles that are always kept clean and carefully handled, and reliability is not of grave concerns. However, the CMC drop-in AR-15 trigger modules are designed to be well-suited to all aforementioned usages without any compromises to reliability under all conditions of usage.

Springs – Another one of the cheap and easy ways to obtain reduced trigger pull weights is with reduced power springs. The springs used in CMC's drop-in AR-15 trigger modules are custom made using the finest music wire spring materials available and are spec'd out to replicate the forces of the springs used in military weapons. This means reliable discharge with inexpensive military surplus ammo, faster hammer lock time to maximize accuracy, and longer lasting reliability in various environments.

Surface Finishing – Other designs use reduced sear/hammer engagement and reduced spring forces to attain lighter trigger pull weights to make up for inferior production methods that can not produce the superior surface finish on engagement surfaces that CMC's state of the art production process achieves.

Materials – CMC uses only the highest grade materials and manufacturing processes available. Each one, the newest materials we are incorporating, the heat-treating specifications and some unique and additional processes not used before in these applications, are the results of intensive studies by a team of highly qualified engineers. No, we won't say exactly what makes all these elements proprietary or others would surely copy us as they have in the past. But we will tell you this:

Extreme Testing – To validate the engineering and design of the newest generation of CMC trigger modules, we implemented an extreme testing protocol. We commissioned an engineering firm to build a machine that replicates the cycle of an AR action. Using this machine, the carefully documented tests include 25,000+ round cycle testing of multiple groups, analyzing each component part and its critical dimensions several times throughout the course of the test. Then the same parts used in the 25,000 round testing, were live fire tested for 500 more cycles and checked again for failures. No cracks, fractures or failures of any kind were found. Therefore, every characteristic of the triggers groups undergo hundreds of thousands of rounds of cycle testing to ensure reliability before we ever release a design update.


Which AR-15 Rifles Are Compatible – The CMC drop-in AR-15 trigger modules are designed to fit any lower receiver manufactured to be within the standard military specifications for nominal dimensions and tolerances, except Colts® with sear blocks.

CMC does offer models of the drop-in AR-15 trigger modules that will fit Colt® brand rifles with larger (.171" diameter) than standard retaining pin diameters. It's always recommended to have an experienced and qualified AR-15 gunsmith to be the one to qualify safe and proper function of the trigger module.


You Can't Go Wrong - CMC will refund the purchase price of any unaltered drop-in AR-15 trigger module within 30 days of purchase. Offer applies to purchases direct from CMC or participating dealers only.

Products returned from dealers to CMC for credit must include proof of the customer's purchase. Refund offer does not include cost of shipping, handling, or other ancillary charges. Participating dealers are responsible for refunding their customers. CMC will be responsible for refunding the CMC dealer upon receipt of the returned products.