AR-15 Triggers- a mini-study
AR-15 Triggers, Single and Two Stage
In an attempt to get a better trigger for my AR-15 Varmint clone rifle, I bought one of the adjustable single stage triggers widely available. It was not the answer. It allowed adjustment of the sear engagement, the over travel, and an adjustment to assure the disconnector function worked properly, as well as the safety worked correctly. When adjusted to minimize creep the gun doubled and when adjusted per their directions, the creep was unacceptable. When the trigger was adjusted to minimum over travel, the trigger would not reset. The limitation of single stage trigger in semi-auto rifles was the basic problem, not the particular one I bought. I am very dissatisfied with this trigger.
The way this AR-15 trigger and other "better" single stage triggers work is the sear engagement adjustment effectively pre-pulls the trigger to get the sear close to the edge of the engagement surface. That makes the gun susceptible to a bump or even the vibrations of a semi-auto mechanism setting the gun off at an inopportune time and makes the gun dangerous unless you dial in some creep. Creep is nothing more than the trigger moving the sear across the engagement surface and when you get it minimized you make the gun potentially unsafe. There has to be a better way and there is… The two stage trigger. More later.
When the single stage trigger system is modified to have less creep it can become less safe if the creep is totally eliminated. So to get to a safe single stage trigger we have to live with some creep to maintain safety in these semi-auto self loading rifles.
Don’t get caught with a gun that doubles or goes full auto. The BATF prosecutes even if the gun got that way by mistake. Who would know and turn you in? How about the guy at the bench beside you or the range master, or the guy several benches down that is your deadly enemy. Test any modification to the trigger system on the bench thoroughly before you shoot the gun with ammo at the range. Prison hurts!
Lets talk about a very common trigger mechanism as used in the M1 Garand, the M1A1, the AKS, and many other guns including the AR-15. It uses a primary sear and a secondary sear (also called a disconnector by some people). The way it works is the primary sear holds the hammer back until you start to press the trigger. The pull of the trigger moves the sear on the hammer engagement surface until it literally falls off, and the hammer falls to ignite the cartridge. As the gun cycles the bolt pushes the hammer back where the secondary sear on the trigger, that is still pulled by the shooter’s finger, catches and holds it. As the shooter releases the trigger the secondary sear looses its grip on the hammer but the primary sear moves to catch it. The trigger is totally released and “reset” and the gun is ready to be fired again.
The two stage trigger works a bit differently. It is so designed as to be absolutely safe normally with lots of sear engagement and yet the final pull, the second stage, can be made virtually creepless. The first stage literally takes all the creep out of the system by allowing the trigger to move the sear right up to the edge where a step increase in trigger pull is easily felt. When the pull is increased to overcome the increase pull level, the trigger barely moves and the sear falls off the engagement surfaces and the hammer falls. In recoil the secondary sear catches the hammer and when the trigger is released it hands the hammer off to the primary sear.
The classic way to get one of these triggers to be a two stage trigger when it was originally a single stage trigger is to use the secondary sear spring to add the extra pull force to the system. The way it is done is the trigger parts are modified (Mostly the secondary sear) so that as the trigger is pulled and when the sear is very close to falling off the edge, the primary sear bumps into the secondary sear. The only way the trigger can move farther is to overcome the spring force holding the secondary sear forward. This is a tricky adjustment as the function of the secondary sear of catching the hammer in recoil cannot be compromised, nor can the secondary sear’s job of handing off the hammer to the primary sear as the trigger is released.
The sear engagement surfaces of both the sear and the hammer must be free of machining marks and well polished with a smooth stone or the first stage will be gritty as the sear is dragged across the hammer engagement surfaces. Some of the European gun versions of the two stage trigger (their favorite!) even chrome plate the sear surfaces so the effect is as smooth a release as is possible.
Once you get used to two stage triggers you no longer will like single stage triggers. If done right, the step from the first stage is just enough so you know when to stop taking up the slack (actually removing the creep) and concentrate on a perfect pull into the second stage which appears to have zero creep.
It is sometimes possible to modify the original parts to a two stage trigger but for the AR-15 guns you can buy a two stage trigger that uses the above method. I intend to buy one of those and install it as my attempts on my original didn’t work out satisfactorily nor did the after market single stage trigger. It is weird but I no longer like single stage triggers regardless of how light they are. Two stage triggers is where it is at! The one on my European Olympic style 22LR target pistol is to kill for!