AR-15 Triggers- a mini-study

Discussion in 'Technical Questions & Information' started by LDBennett, Nov 11, 2009.

  1. LDBennett

    LDBennett Well-Known Member

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    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!

    LDBennett
  2. new308handloader

    new308handloader New Member

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    Very informative LD!...and very well written…thanks for taking the time.
    I currently have a Jewell trigger on my AR which I assume now must be a single stage. Would a two stage trigger be best for varmint / target shooting Vs. hunting or self defense?
    Also, not sure if you shoot groups…but have you noticed a decrease in your group size with the two stage trigger? …..or if not shooting groups do you hit more small furry animals when “varminting”?
  3. GunHugger

    GunHugger Well-Known Member

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    Great post LD. :cool:
  4. LDBennett

    LDBennett Well-Known Member

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    The two stage trigger is on order and not yet installed but I have several guns (mostly European) with them and they are much easier to control when shooting groups on targets.

    The point I was making was that single stage triggers with little creep and light pulls are dangerous as all the safety of large amounts of sear engagement (creep) is gone. It is particularly unsafe in a semi-auto weapon like an AR-15. With the dual stage trigger done right you get the safety of lots of engagement and the sweetness of a no creep letoff. Trigger pull level is not as important as a good letoff and the two stage trigger can have a good crisp letoff like a finely tuned single stage and be maximally safe when the trigger is not being pulled. Most American shooters do not appreciate how really good a two stage trigger can be or appreciate the safety it gives to a weapon.

    I do have set triggers on my CZ's, which when set have extremely light and crisp trigger pulls. I not only find then hard to use when set to ounce levels buy find I can sometimes shoot them better when the triggers are not set and operate just like any other good single stage trigger at 1 to 3 pound trigger pull levels. The light single stage pull, for me, is hard to control and know exactly when the trigger is going to release the hammer or striker. The anticipation of an unknown release point can give me the shakes trying to control the trigger. This may well be just my problem but the two stage seems like my answer and it could be the answer to others as well.

    LDBennett
  5. new308handloader

    new308handloader New Member

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  6. Bobitis

    Bobitis Guest

    LD, what did you order?
    I have a RRA 2 stage match trigger on one of mine, and it's the cats pj's.

    I also did a mod on another that only requires a few steps. It doesn't eliminate the creep, but makes it much smoother and predictable.

    Great post!
  7. LDBennett

    LDBennett Well-Known Member

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    Bobitis:

    A Rock River Arms two stage! The one I'll be taking out is the adjustable JARD single stage. I might have used the JARD two stage but they didn't answer my email or their phone.

    LDBennett
  8. Bobitis

    Bobitis Guest

    Pretty sure you're gonna love it. Mine is sweet.:D
    And a LOT less than the JARD.;)
    Reading on the JARD made it sound painful to install. I build my lowers, and the RRA trigger was no more difficult than the regular triggers.

    Let us know what you think when you get it.:)
  9. LDBennett

    LDBennett Well-Known Member

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    Installation Report of Rock River Arms Two Stage trigger in AR-15

    I got the trigger from Brownells and installed it today and here is what I found:

    I installed it out of the box but the pins were "oversized" (by design). They were 0.1555 inches and stock pins are suppose to be 0.1540 inches. The instructions say to grease them up and force them into the receiver holes. I had trouble with that whole concept. Swaging my receiver out to those bigger holes would not ever allow me to go back to any other trigger system and those pins might not fit through anyone else's trigger parts. So I used the original Mil Spec pins. There was very little movement laterally of the RRA trigger parts on the smaller stock pins when installed in the receiver. Not using the RRA oversized pins appears to not had an adverse impact on the trigger pull.

    The first stage measured 3 1/2 pounds and the step up to the second stage was another 3 pounds for a total of 6 1/2 pounds although it didn't feel much like a 6 1/2 pound trigger. I was not satisfied.

    I reshaped the trigger return spring by trial and error and finally settled on a first stage pull of 2 pounds. Any less and the trigger return spring could not always over power the friction of the system and fully return the trigger forward after a partial pull. The resultant pull was 2 pounds first stage and an additional 3 pounds for the second stage for a total of 5 pounds. That seems like a lot but all you really notice is the increase once you get to the beginning of the second stage.

    There seemed to be a minute bit of roughness so I very very lightly stoned the primary sear surfaces on the hammer and the trigger, adding a bit of moly grease to both sear surfaces and to the nose of the primary sear where it bumps into the secondary sear. The pull didn't change all that much but felt smoother. The let off is very crisp.

    I like this trigger. My only comment is that the secondary sear spring seems a bit heavy (which effects the weight of the second stage) but it seems to be riveted onto the trigger, not allowing modification of the pull level for the secondary stage. But as a Tactical Match level trigger, which it is sold as, I think it worlds better than the adjustable JARD or the stock trigger. I would like a little less pull for the second stage but I don't think the way it is now will be detrimental to my varmint version of the AR-15.

    I suggest anyone who does not understand trigger system and/or is not a gunsmith to NOT make the modifications above (it kills the warrantee) to the RRA two stage trigger system. Install it box stock and live with it but it would not be hard to live with. The trigger right out of the box is not all that bad, certainly better than stock, and a lot safer and more creep free than the adjustable JARD single stage trigger. The JARD leaves you with a compromise: safety or minimal creep with the possibility that the gun will double (believe me I know!). The pricing on this RRA Match trigger is significantly better than any other two stage trigger I could find.

    Hope this helps.

    LDBennett
    Last edited: Nov 14, 2009
  10. Bobitis

    Bobitis Guest

    Good stuff LD. Thanks.

    My trigger was purchased along with my lower. It went together smoothly.
    I suppose the lower was already matched for the trigger. I've no way to determine pull wt, but the RRA trigger is FAR better than the stock trigger.
    I'm quite mechanically inclined, and little things don't bother me much. Messing with triggers has its consequences.

    Good advice - great topic.

    Thanks again.:cool:
  11. LDBennett

    LDBennett Well-Known Member

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    Bobitis said:

    "Messing with triggers has its consequences."

    I am very mechanically inclined (graduate engineer) and always think there is a better way to make anything. I can not stand to use a gun with a poor trigger when I know how to make them better and safer thanks to the American Gunsmithing Institute's general Trigger Jobs course and 20 years of fooling with guns. The AGI course was 10 hours longs and very comprehensive but very expensive. I got it before that last price increases but it was still expensive. The bottom line is almost every gun I own has had a trigger job to some extent, and it might just be adjusting the adjustment included in the original trigger system.

    The results of adding the RRA Two Stage Trigger to my AR clone was rewarding. I recommend this trigger. I do not recommend the JARD Single Stage Trigger I removed. If JARD had been more customer aware (didn't answer email or their phone) I might have been praising their two stage trigger system. They loose!

    LDBennett
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