$35 DIY AR Trigger Job

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  • TennJeep1618

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    I started to put this in the gunsmithing section, but I figure it is more applicable here.

    I'm sure this is not news to most people familiar with building and modifying an AR platform, but I found a way to get a pretty decent trigger without spending big $$$ on a drop in. Of course, I forgot to take pictures when I did this, but I will do my best to substitute.

    I started off with a basic mil-spec trigger that comes standard with most LPK's. I polished the sear surfaces, then I cut the tail off the hammer.

    It looks like this with maybe just a little more metal left on it.

    hammer-mod0_zps3d6f64a3.jpg


    After that, I installed the JP Enterprises Reduced Power (yellow) Spring Kit and re-installed the trigger group.

    JP-JPS3_5-2_zpse2dc1e6e.jpg


    After installing the JP spring kit, the trigger pull was significantly lighter; however, there was still quite a bit of creep. I read where some people have tapped a hole and installed a set screw under the safety to reduce the creep. I considered doing that until I found this:

    JB-TRIGGERADJUSTER-2_zps5ab42de6.jpg


    This "trigger adjuster" utilizes a set screw inside a replacement grip screw to reduce creep. Basically you install the grip screw as normal, then use the supplied allen wrench to tighten the set screw inside until it stops. At this point, the safety selector should not be able to move. Then you back off the set screw 1/8 of a turn at a time until the safety selector moves freely. At this point, most of the trigger pre-travel should be gone.

    I don't have a trigger pull gauge, but I can tell that the pull is significantly lighter, smoother and with less creep.

    I did this to my AR in January and have fired over 500 rounds since then without any hiccups. I just finished doing the exact same thing to my dad's AR last night for his father's day gift. I've never fired an AR with an expensive drop-in trigger group, but I'm sure this trigger "job" is nowhere near as nice as those. It is, however, a huge improvement for not much $$$.



    I bought the JP spring kit from Gold Mine, but both the spring kit and the trigger adjuster can be found here for less than $35 shipped:

    http://www.joeboboutfitters.com/JP_AR_15_REDUCED_POWER_SPRING_KIT_p/jp-jps3.5.htm

    http://www.joeboboutfitters.com/JoeBob_s_Trigger_Adjuster_p/jb-triggeradjuster.htm (Edit: They have changed the trigger adjuster screw since I first ordered mine. I recommend spending the extra $4 and getting the hex driver that they offer. You can use a standard 1/16" allen wrench, but most of them are nowhere near long enough to reach all the way to the set screw inside the grip.)


    I'm about to go on vacation, but I'll try to remember to take everything back apart and get step-by-step pictures when I get back. Until then, I'll be happy to answer any questions.





    I finally got around to taking the pictures I said I would. Here is a link to the post further down in this thread: http://gulfcoastgunforum.com/showthread.php?9814-35-DIY-AR-Trigger-Job&p=102307&viewfull=1#post102307



    Now with Video!!!

    https://youtu.be/pCPLe6FwNkQ
     
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    Robbie2883

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    if you get a good lpk then you shouldn't have any creep or need to polish(i like cmmg lpks)...BUT the jp springs are a great replacement over any stock springs.
     

    TennJeep1618

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    if you get a good lpk then you shouldn't have any creep or need to polish(i like cmmg lpks)...BUT the jp springs are a great replacement over any stock springs.

    Both of the one's I've done this trigger job on were PSA lpk's.
     

    Robbie2883

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    i've never installed a PSA kit....not even in the psa lower i have. lol while i love their lowers,from what you're stating i wouldn't want a PSA kit. next one you do snap some pics.

    btw...i'm not trying to knock what you have done by any means. it's all good info because all ar's are not built the same. out of curiosity was there creep before you did any polishing? just curious.
     

    TennJeep1618

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    i've never installed a PSA kit....not even in the psa lower i have. lol while i love their lowers,from what you're stating i wouldn't want a PSA kit. next one you do snap some pics.

    btw...i'm not trying to knock what you have done by any means. it's all good info because all ar's are not built the same. out of curiosity was there creep before you did any polishing? just curious.

    Yes, there was pre-travel before and after the polishing. The JBO "Trigger Adjuster" set screw, not the polishing, took out almost all of the pre-travel.
     

    JohnAL

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    if you get a good lpk then you shouldn't have any creep or need to polish(i like cmmg lpks)...BUT the jp springs are a great replacement over any stock springs.

    I don't know what you call good but even Colts come with lousy triggers. Mine felt like it had 4 stages and was about 9 lb. As deaf as SAWMAN is he could hear the grit in it from the next bench at the range.
    A procedure similar to what TennJeep did but a little more involved took out the creep, the over travel, and reduced it to around 3 lb.
     

    Telum Pisces

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    My LR-308 trigger is about the most horrible thing I have ever felt. I may get around to doing something like this very soon. I was turned off by the huge price of drop in triggers. It's crazy what those things cost.
     

    TennJeep1618

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    So I finally got around to taking pictures, thanks to a new AR to play with.

    First, here are the stock parts on the right and the new parts on the left.

    IMG_8670_zpsb44ecd0b.jpg


    Here is the new trigger and disconnector springs installed as well as the cut marked on the hammer.

    IMG_8672_zpsb5bdfead.jpg


    Here is the hammer cut:

    IMG_8674_zps69eba1c5.jpg


    Here are all the new parts installed, except for the grip/trigger adjuster screw.

    IMG_8676_zps74b97d5c.jpg


    Everything installed:

    IMG_8680_zpsa405a37a.jpg


    Picture of the bobbed hammer after installation:

    IMG_8682_zps489ba97d.jpg


    I'm going to test fire everything tomorrow to make sure it all works, but this method has worked 100% of the time in the last two installations.
     
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    TennJeep1618

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    Just curious, but what does bobbing the hammer do for you?

    The JP yellow springs are lighter weight than the standard springs, so the hammer moves slower due to less spring tension. Bobbing the hammer removes mass, letting the hammer travel faster even with the lighter springs. I had a few light primer strikes when I first did this mod and left the hammer whole. Since I bobbed the hammer I have had 100% reliability.
     

    TennJeep1618

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    I wanted to update this thread. I got a trigger pull gauge last week and just tested all the AR's that I've done this mod to. The two mil-spec triggers are sitting at 4.5lbs and the ALG QMS trigger is at 4.75lbs.
     

    CCHGN

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    Just not sure if the same treatment will work reliably on a 308 AR.

    yeah, I'm on the M14 Forum and there's a group that's doing that to M1A's. ( For long range shooting) They're making the hammer as light as possible( the idea is that the minimal movement for better accuracy, think[but not really sure]).

    The thing for me is, the job of the trigger is to 'break' the sear from the trigger, what happens after the sear breaks is after the fact. The spring on the trigger is for the return, right? I don't so much want to lighten my trigger as much as make it smooth to the break. I'll polish the two pins and inside the trigger and hammer( and grease 'em) and where the sear and trigger meet.

    Am I missing something?
     

    Droshki

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    Please forgive me if I'm totally off base here, as I do think this is a neat idea, but doesn't lightening the trigger springs, and reducing hammer mass, greatly increase the odds of light primer strikes?
     

    TennJeep1618

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    Please forgive me if I'm totally off base here, as I do think this is a neat idea, but doesn't lightening the trigger springs, and reducing hammer mass, greatly increase the odds of light primer strikes?

    Cutting the hammer should actually prevent light primer strikes.

    Since the JP springs are made to have less tension than stock springs, the hammer accelerates slower than it normally would, sometimes resulting in light primer strikes. When you bob the hammer, it removes mass which enables those lighter springs to accelerate the hammer faster than a stock hammer. It's all about force, acceleration and mass and a primer requires a sharp "strike" rather than a slow "push".

    Think about it this way: Compare you (stock spring) pushing a motorcycle (stock hammer) to a kid (JP springs) pushing a bicycle (lightened hammer). You can both (for this instance) push your respective 2 wheeled vehicles at the same acceleration rate. If the kid (JP springs) were to try to push the motorcycle (stock hammer), it would accelerate much slower than them pushing the bicycle (lightened hammer).

    Does that analogy make sense?
     
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    Umma you lost me. They sell a reliablity jp kit, has a red hammer spring. The reliablity kit is better to me because you don't have to cut the hammer and the trigger weight were the same. At least I couldn't tell between the two.
     

    JohnAL

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    You can take anything too far but the JP springs have a great reputation. I did not bob my hammer and the rifle has been flawless with all kinds of ammo including Russian.
     
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