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AR15 Troubleshoot that will hopefully help others

Discussion in 'Gunsmithing and Repairs' started by savhmustang80, Apr 4, 2013.

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  1. savhmustang80

    savhmustang80 Member

    Jan 9, 2013
    Cape Coral, FL
    I wanted to post this in the event that it may help out someone else as I found the thread posts surrounding this subject very helpful while troubleshooting my brand new AR problem. Kind of a long post, but honestly, I haven't seen too many threads duplicating this same issue with an AR, and the other threads really helped me get to this point.

    Firstly, a description of the rifle- standard AR15 20" flattop set up.
    Lower is Rock River Arms.
    Lower internals were DPMS
    Upper was an FN barrel 1/7 twist from PK Firearms. One of the machine gun
    steel barrels. Believe the receiver to have been either an RRA or Colt
    overrun. I honestly haven't gotten to the point of pinpointing that yet.
    BCG is RRA. Both the upper and BCG purchased together.

    So once I got my upper out and cleaned up, assembled, off to the range I went when lo, and behold, I found myself to be the proud owner of a single shot AR. Much embarrassment. So I went online, did my research, and most posts indicated that it could be a gas system issue. Essentially, what was appearing to happen was I would fire a shot, and the bolt did not appear to be going back into battery. Manually eject the round, chamber the next, and same thing.

    Researching the issue I believed it to be undergassed initially. But in reading the multitude of posts I checked to ensure my gas keys were staked (they were- amazing how many people point to this as the first item to check), checked to ensure the gas port on the bolt lined up with the gas line (it did), checked to ensure I didnt have some stray bit of cosmoline fouling up the gas port in the barrel (it wasnt- checked by blowing compressed air down the gas line and could see it exiting when viewing down the barrel (precluding the need to ensure that the gas line wasn't mounted 180 from normal)), checked to ensure my gas rings were not all lined up (well 2 were but I fixed them), and then took it back out to the range to see if the bolt would stay back when firing only one round from a magazine (it did). I also worked the bolt about 200 times just to ensure I wasn't getting brand new metal on metal retarding the movement of the bolt. Oh, and I lubed the hell out of it with CLP per all those recommendations to "break it in wet" (not a fan of that- been the recepient of way too many pushups at Parris Island for an over lubed rifle).

    Ok, so I am thinking I am good to go. Load up a full magazine, ready to fire away and get down to zeroing. Bam. One shot. So I go through and manually chamber a few more rounds and feel something off in the trigger group. The slightest of movements. I flip my safety from safe to fire again, bam. Pull the trigger again. No shot. Flip the safety again, and I get a shot, again each time. So now I know my problem is localized to the FCG in the lower which is causing the trigger not to reset. I take things home, pull the lower apart and reput it back together. Upon examining, I am 99% confident that I put it in correctly the first time (oh so many threads concerning the subject of springs put in upside down), but I do it all over again. Take it to the range. Test fire. Still having the same issues.

    I am talking to the RSO while I am there, with my rifle stripped apart. Let him fire it a few times and he notices the same thing. Take it apart again and we start examining the internals. He notices that the hammer from the DPMS parts kit has what appears to be the smallest of mis-cuts where the hammer engages the disconnector, almost just a burr of metal. He said he had seen this issue with AK's before, but never a AR. I personally had never seen it before either, but then again all my experience with the platform- they had either been well used or the 3 I had built previously (and that's not a large sample) worked fine after assembly. So given its a RRA lower, I ordered a RRA FCG set and put in it. Take it to the range today and it's all smiles- works flawlessly. On top of that, the upper is already pretty much zeroed in for me.

    Things I noticed comparing the RRA vs DPMS FCG's- the hammer and the hammer spring were noticibly different. The hammer spring in the RRA set was much more robust. Thicker spring, tougher, looked just like the spring I used on my M16 in the Marines. Comparing the hammers- the DPMS hammer was heavier, notchless on the top, and did have just the tiniest bit of extra meat on the hook that engaged the disconnector that was causing the problems. Also the pins holding the FCG in in the RRA set were just a bit tighter (good thing). Other than that- everything else was the same.

    As for that DPMS hammer causing the issue- I am filing down that little miscut, going to test for functionality, and then stowing it and the other FCG parts in the event I may need them down the road. Hopefully this post helps someone out! Now I got to zero in my USMC RCO ACOG for it!
  2. rcmodel

    rcmodel Member in memoriam

    Sep 17, 2007
    Eastern KS
    All well and good.

    But I can tell you right now if you have to stagger the gas ring gaps on a AR-15 bolt to get it to work?

    Something else is badly wrong with it.

    The gas rings are continually moving every shot.

    And if they start out staggered 120 degrees, they won't be 100 rounds later.

    A properly working AR will still be a properly working AR with the gas ring gaps aligned, or a whole gas ring missing.

  3. savhmustang80

    savhmustang80 Member

    Jan 9, 2013
    Cape Coral, FL
    Gas rings

    Oh, I don't doubt that they would work, and do work, just initially when I thought it was a gas issue, and trying to get my rifle to work, one of the recommendations I saw was ensuring the gas rings were "properly" aligned. I guess I was thinking that it could be one of those combined issues where a mass of incremental issues added up causing the rifle to fail to completely return to battery (which wasnt the case at all). That was one of the recommendations to check that I saw on actually many boards.

    Brand new rifle, lots of money spent, you kind of grasp at everything to get it working! When I was in the Corps I honestly never really paid attention to those gas rings, how they were staggered, etc. The rifles just worked no matter how they were staggered, and they never really wanted us messing wtih them anyway. Just scrub them down and make sure they had a very thin film of CLP around the part.
  4. gprisock

    gprisock Member

    Jun 2, 2013
    I have built 3 AR's and took al 3 to the range today 2 of the 3 fired perfectly the 3 would act like a single shoot not extract the round. I think I have improperly seized gas block here are the barrel specs and the gas block.

    -.223/5.56 Caliber
    -M4 Profile
    -1:7 Twist Rate
    -1/2x28 Muzzle Thread
    -M4 Feed Ramps
    -Carbine length gas hole
    -.750" Gas shoulder


    This gas block replaces your existing front sight to provide a simple,
    low profile design that can be used to mount a rifle length forearm to a
    carbine length barrel. It is mounted by the use of two set
    screws (YHM-9383) and is .950 Inches
    long. Manufactured from high quality steel and finished with a mil.
    spec. phosphate coating. Made in the U.S.A. This gas block has a bore
    diameter of .750 inches.
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