Triggers are a popular subject in the AR world, though the debate is not nearly as involved as with barrels. In truth, triggers are a huge personal preference. The only hard concepts to keep in mind is the original two laws:
1. Let the mission drive configuration
2. Buy Once, Cry Once
There is a trigger to suit just about any particular need you may find yourself with. Two overarching types of triggers rule over all others: single stage and two-stage. Within these categories, there is a variety of weights, trigger bows, and material selection.
Single stage triggers are, by far, the most common type found in the AR-15 platform. Nearly every military issued rifle is equipped with a single stage trigger. The majority of rifles sold on the civilian market come equipped with a basic single stage trigger. It is simply the most common. That doesn’t mean that the single stage is worse in any way, there a many precision and hunting rifles on the market with this type of trigger.
Interestingly, the M16 is the only single stage trigger in the recent history of military rifles. Single stage triggers, up until the M16, were considered precision triggers more than combat triggers.
A single stage trigger is fairly basic. There should be no (or very little) slack during the takeup. The full weight of the trigger is already resting on the spring; the shooter simply must overcome that initial weight. The trigger bow is directly connected to the sear. If there is a lot of surface engagement to the hammer, then the shooter has to “walk” through the sear engagement until it finally disengages and the hammer is released. This slight movement as the sear is disengaging is commonly referred to as “creep.”
Note the notch at the bottom of the hammer, where the front end of the trigger piece (the sear) fits into. This is what you are overcoming during a single stage trigger press. The hook to the rear is the disconnector, which ‘catches’ the hammer as the weapon cycles and stops it from going forward again as the bolt carrier passes (if the trigger is still being held down). The distinct ‘click’ you fell when you release a trigger after the shot is the disconnector letting go of the hammer and the sear reengaging for the next shot.
Common hunting and precision rifles in the bolt gun world use single stage triggers with light pulls (4 lbs or less). In order to get a crisp trigger pull, there must be a minimum amount of sear engagement for the shooter to overcome. For a light pull, the springs and engagement must be machined as to not provide minimum resistance. A light/crisp pull was deemed too dangerous for a combat rifle likely to get bumped around and mishandled by the average GI. To compensate, the pull weight was raised to a range of 5.5 to 8.5 lbs with a healthy amount of sear engagement.
Single stage triggers are popular due to their quick operation and simple design. All things being equal, a good shooter can probably shoot slightly faster with a single stage trigger. A light/crisp single stage trigger can be designed to operate safely, but it will add to the cost of the unit. This cost is why a quality single stage is so much more expensive than the standard mil-spec trigger.
Two Stage Triggers
Two stage triggers are characterized by a short and initial take up, followed by a slightly heavier ‘wall’ to overcome before the shot breaks. The total weight of the trigger will be divided between the two different portions of the trigger pull. For instance, a 4.5 lb trigger might have a light 2 lb uptake followed by an additional 2.5 lb ‘wall.’ This provides a bit of safety “slack” for the rifle to be bumped around as well as a very predictable break point for the shot.
Two stage triggers are common for a lot of shooters because it allows them to begin applying light pressure to the trigger in order to “prep” or “stage it,” once they are riding along the ‘wall’ of the two stage, they can wait for their sight picture to settle and simply apply just a little bit more pressure and fire the weapon.
Here is a typical two stage trigger, notice the different position of the sear relative to the single stage. Note that in the first picture I posted of two stage, the Geissele still has the original notch at the bottom of the hammer. Bill Geissele calls this the ‘half cock’ position (like a 1911), and leaves it as a safety feature in the event the actual sear disengages without the trigger being pressed
The downside with this, as I have found out many times, is that a sufficiently light second stage combined with a momentary lack of awareness can cause the shooter to accidently bump past the trigger’s wall prematurely, sending the shot off target.
Overall, a two stage trigger will have lower perceived pull weight before firing when compared to a single stage trigger. This happens because on a 3.5 lb trigger, you will pull through the first 2 lbs during the take up and feel a notable, but very light, 1.5 lb wall before the shot breaks. In contrast, with a single stage trigger, you will feel all 3.5 lbs up front with no movement (ideally), and then the shot will break.
Tips For Choosing
In all honesty, this is personal preference. There are a wide variety of triggers on the market catering to different uses. The big thing to keep in mind is that you get what you pay for. I have seen many inexpensive two-stage triggers from a well-known company fail within a few thousand rounds due to soft case hardening wearing through. In contrast, triggers like those from Geissele or Wilson have proven to have both an excellent feel and be extremely durable. Do your homework ahead of time.
Remember, everything is a compromise. Extra crisp triggers require extra time in machining and tighter QC tolerances, which mean higher cost. Super light triggers can work great for target shooting competitions, but might be inadvertently activated by a shooter who is under stress and an adrenaline dump (hunting, self-defense, action shooting), resulting in a missed shot. Or, even worse, poorly designed light triggers may release if the rifle is bumped or dropped- obviously bad.
Most people are well served by a quality mil-spec trigger like those from ALG (the QMS or ACT). After everything else is dialed in skill wise, then consider upgrading the trigger if it is needed at all.
The bottom line is you should decide what use you need your trigger to fill, do your homework on the options, and buy quality. However, do not use the trigger as a crutch for bad fundamentals.