Note where the disconnector hooks behind the hammer. If the drift pin hole for the hammer is farther forward it wont engage and the weapon becomes full auto. Farther back and you have a long reset, or the rear of the hammer will just bounce off the disconnector rather than engage, making intermittent bursts or soft strikes.
The standard AR-15 trigger was designed to provide a satisfactory pull and reset with a solid hammer strike onto the firing pin. It does that job very well. It was not designed to be customizable into a hair trigger with a featherlight pull and tiny reset. The very system that attaches the trigger set up to the lower makes tuning the trigger to perfection difficult. Even a tiny fractions of an inch of difference between the drift pin hole location on a lower can alter a perfect trigger into crap trigger, or worse, into a dangerous/illegal trigger.
Several mechanical geniuses working for several brands have sought to solve this issue and for the most part they have...
... Enter the after market fire control group. While an AR trigger may never match some of the best bolt gun triggers, you can still get a pretty sweet set up.
The standard AR trigger is single stage. Yes, you can usually feel some slack when you first start your squeeze but then it should break once the slack is out. A double stage trigger may also have some slack, but then you feel an increase in resistance then some more movement and then the shot should break without any further feel of pressure against your finger.
The best way I have heard it explained was that a single stage trigger should feel like you are breaking a glass rod. No movement, just a crisp snap. A 2 stage trigger should feel like you are pushing a mug off a coffee table with your eyes closed. You push with a steady movement and suddenly it goes.
It is really, really hard to tell someone if single or 2 stage is a better trigger for them. If you love your AR trigger and just wish it had less movement, stick with single. If you are a disciplined shooter with solid shooting fundamentals and you want the break of the shot to be a surprise, try a 2 stage trigger.
Myself, I like both. For rapid shooting I prefer the single stage and for longer range shooting I prefer 2 stage.
That is one question I can’t answer with great certainty. I have shot many different triggers, but I feel that among the top triggers I would need to get 2 lowers that are close to identical and try every trigger in each lower, comparing them all over time. That is an expensive project. What I can do it give some impressions and list the top triggers in each category.
Please don’t take this list as complete or gospel: These are not solid comparisons, they are impressions gained over some time (years). Memory may have faded and more importantly, I did not get to set all triggers myself or adjust them. With time and money I will dial in this list.
JP EZ trigger. Great trigger, maybe the best. (I currently own 2)
AR Gold. Crisp break, short reset. Also great. (Tried some time ago)
Jard. Very nice. The one I used was very, very light (Briefly)
JP Adjustable Trigger. Best value trigger if you have the time to tune it (still own one)
Chip Mccormick. Solid improvement on stock triggers (Tried some time ago)
Timney. Awesome look, nice trigger (Tried some time ago)
Jewell, Very nice in my opinion a little better than the Giesselle (tried 6 months ago)
Giesselle. Still very nice and smooth (own 1)
Armalite. Ok for the price (tried some time ago)
Rock River. Not worth it.
I have yet to try but want to based on internet research: Accuracy speaks (I have my doubts but I am curious), ALG defense, Compass Lake Engineering (unique use of safety to make 2 stage) and Wilson Combat (some good reviews from buddies).
Lucky for you, you have options. You can take your trigger out and polish where the trigger meets the hammer (the sear) and where the disconnector meets the hammer using the finest emory paper you can find, or even just some old leather if you are insanely patient (or have too much time to kill on a deployment). The idea is not to remove any more material than is needed to make an ultra smooth surface. But you can also mess it up and make it worse. Some strongly advise against the use of an abrasive as strong as emory paper, but I have used 3M's 2000 grit and it worked well. Alternatives are many and include even toothpaste. Or you can try just dry firing you trigger until it is smooth. In my experience that technique is slow and less effective than use of a mild abrasive.
You can also bend your springs to remove some tension, buy lighter springs and/or even grind your regular hammer from behind until it becomes a home made speed hammer. While these things are all doable, I am not comfortable yet about putting my name on how to best do it. I used the internet, youtube and the help of an armorer to learn how. For a quick reference you might try the 15 minute trigger job. I truly wish you the best on what can be a satisfying endeavor A final tip is if you know you are impatient and you are using anything more course than 2000grit, order at least buy an extra disconnector before you try it.
***** WARNING ***** Messing with your trigger if you don't know what you are doing can make your rifle dangerous, unreliable or illegal. It is imperative that you have a thorough understanding of your trigger and how it works before attempting to make any adjustments to it.