AR-15 double burst problem

Discussion in 'Technical Questions & Information' started by jlloyd73, Nov 28, 2010.

  1. jlloyd73

    jlloyd73 Active Member

    Nov 28, 2010
    I have an AR-15 that will sometimes shoot a double burst. There have been no modifications done to the weapon. I need to know what might be the problem so I can narrow down the problem. Not a problem for me really, but my brother was concerned about federal law. With that in mind, if there were no modifications done, could there be a legal issue here.
  2. armedandsafe

    armedandsafe Guest

    By federal definition, you now have a machinegun. Yes, there is a legal problem.


  3. muddober

    muddober Active Member

    Sep 19, 2008
    Carson City Nevada
    As for the law I would not concern myself with that a s much as the fact you have an unsafe situation going on. When you say AR 15 do you mean Colt? Did you buy the gun used? The real early Colt AR 15 bolt was solid from front to rear where the hammer rides just like an M16 bolt and I have seen that heavier bolt cause a slam fire but it is very rare unless you take the disconnecter out of the gun and then it will go full auto but not just one or two rounds, more like five or six before you can get your finger off the trigger. But again it will only do it with the old solid bolt. The newer bolts have a slot cut in them that allows the hammer to go up into the bolt jamming it so it will not slam fire.

    What all this means, I would need to see pictures of the parts to your gun to help you with the fix. Perhaps some one else here may have a better idea but I have to say I have been playing with AR 15 since they first came out in 1962 when I paid $163.00 for mine serial number XX2. I would also like to see the primer on the third round that the bolt picked up but didn't fire. I am assuming third round because you mention that the gun only doubles. Does the gun completely chamber the third, meaning can you pull the trigger after the doubling event and the gun will fire. If so I need to see that primer unfired.


    I just read Pops post and in a broad sense he is right, meaning the definition of a machine gun is any gun capable of firing more than one round with one continuous pull of the trigger. In a narrow sense you have a gun that is malfunctioning and unless someone has played with the gun internally I doubt you would go to jail. Again I would be more concerned from a safety standpoint. I think any gun firing a round on its own when you are not expecting it is unsafe.

    Lets see if we can help you fix it and any legal issue will be fixed as well.
    Last edited: Nov 28, 2010
  4. Toolmanroberts

    Toolmanroberts New Member

    Sep 16, 2010
    I would just like to add that my friends AR-15 would do the same thing as yours if the bolt got really dirty. His would often fire 5 to 8 rounds before you could get your finger off of the trigger. It is a DPMS Panther in 223. He bought another bolt for it [titanium I think] but it will do the same thing when dirty.
  5. muddober

    muddober Active Member

    Sep 19, 2008
    Carson City Nevada
    While I am not too familar with all of the different AR15s out there and I would have to guess that the guns doing that must have old style if not even perhaps M16 bolts. An M16 bolt in and of itself is no different that the early bolts with the exception that the early bolts lacked the serations for the forward assist. The first guns that went to Nam did not have forward assist.

    Last edited: Nov 29, 2010
  6. ALLONS11

    ALLONS11 New Member

    Jul 3, 2008

    I've seen a few ARs that fire 2 shot bursts. Sounds like yours only fires 2 rds, not 3 or more. If this is the case the first place I'd look is at the hammer, disconnector and trigger timing.

    If the disconnector hook doesn't hold the hammer back after the first shot till the trigger ledge can lock into the bottom of the hammer, it would be the sear area on most arms, the weapon will fire a second shot when the trigger is released.

    When you pull the trigger it fires, when you ease off on the trigger it fires again. With a normal trigger pull this can happen so fast it feels like full auto for 2 rds.

    An easy way to troubleshoot this is to (A) pop out the takedown pin and pivot the upper down to allow access to the lower FCG parts.

    (B) Grip the hammer & pull the trigger, don't release the trigger yet! (C) The hammer will fall forward, now with the trigger still pulled, push the hammer back till the disconnector hook locks the hammer back.

    (D) Now if there is a problem when you release the trigger, the hammer will fall again, (second shot on one trigger pull).

    Now that the trigger is released, push the hammer back again, the trigger notch catches the hammer and everything is normal untill you pull the trigger again. Thats why it will only fire 2 shots and stop.

    I'm not saying this is your problem, but it is the first place I'd check. If all is OK in this area then you can rule it out. I've seen this situation caused by parts wear, out of spec FCG parts and even out of spec lowers.

    As far as a legal problem, I think so, but WHY take the chance? When the lawyers get involved, common sense goes out the window. Also if you would have the condition described above, the shooter fires one rd. If the shooter still has the trigger pulled and turns the weapon your way, when he releases the trigger its gonna fire again!:eek:

    Good luck solving your problem, Ken
  7. jlloyd73

    jlloyd73 Active Member

    Nov 28, 2010
    I will take the gun out in a few hours and pop a few rounds off and get some pics on here. I am curious to mudbober's question on the third round, so I want to get a pic of that first. I will also post some pics of the bolt assembly, and trigger group.

    Sometimes the gun will do a double burst with the first few rounds out of the gun, and sporadically after that. Sometimes I can shoot half a clip with nothing and then it will start doing it.

    I don't shoot the gun as much as my son does, but I am pretty sure it will do a double tap with one smooth pull...and not on the release of the trigger, but I will do that test as well to rule that out.

    I am asking more of the legal question because when my brother came out to shoot this weekend he was convinced that I had modified the gun. All I could explain to him was that it was a factory single stage trigger group. I didn't know if this could be easily explained...because I didn't want him or anyone thinking I would modify the gun. I enjoy semi auto guns just fine.
  8. Helix_FR

    Helix_FR Active Member

    Apr 14, 2009
    Imperial, MO
    This is just reaching here but I have seen it before but is it possible that your actually firing 1 round on trigger pull and 1 round on trigger release? It may go unnoticed to you but recoil can allow your finger to let up enough to drop the hammer out of the disconnector. Now most times the trigger sear would then catch the hammer hook and stop it as it normally would but if the hammer pin hole and trigger pin hole are slightly too far apart (and yes I've seen this and I'm talking about .010)or the disconnector is worn the disconnector won't hand off the hammer properly to the trigger sear and it will actually fire again on let up. To check this, fire one round and squeeze the trigger hard to prevent your finger from bouncing off. Then slowly let off the trigger and i mean really slow. If you hear a click, then it handed off and thats not the problem, if it goes bang then the disconnector needs to be replaced or needs to be adjusted for more engagement to the hammer so it hands off correctly.
  9. Helix_FR

    Helix_FR Active Member

    Apr 14, 2009
    Imperial, MO
    There is some leniency (very little) IF the gun malfunctions and the problem is address right away AKA, your at the range, it goes auto, you don't shoot it anymore and have it fixed. There is no leniency if you keep shooting it with that problem. And believe me, they will know. If its bursting, get it fixed. Don't mess with it, don't think its OK, don't hope it don't do it no more, just fix it.
  10. LDBennett

    LDBennett Well-Known Member

    Dec 20, 2003
    Hesperia, CA

    A simple test is to separate the upper from the lower and put the upper aside. Push the hammer back till it cocks. Pull the trigger and hold the trigger back. The hammer should fall. With the other hand push the hammer to the rear and let the secondary sear catch it. Now release the trigger and the primary sear should catch the hammer and hold it cocked. Repeat this in slow motion and see if there is a place where the transfer of the hammer from the secondary to primary sear fails to catch the hammer. This transfer is manufactured into the trigger assembly but maybe the edge of one of the sears is broken off or otherwise not per spec. Replacement of the trigger/sear parts will more than likely fix it if this is the problem. There is a spring that controls the secondary sear and it may be collapsed or broken or missing. But firing the gun is not necessary to isolate this problem, I would think.

    All it takes is for a shooter at the range to note that your gun is doubling and you are continuing to shoot it. If he is a A-hole he can report you to the BATF (using your license plate or the sign-up sheet). The BATF loves to prosecute us law abiding gun owners as we are easy to find (own homes, own cars, have jobs, vote). If the gun fails and doubles but you quit shooting it the BATF usually doesn't care. But if you continue to shoot it doubling they will prosecute. It is a legal problem now because you detected it was doubling and you continue to shoot it. If you don't have the know-how to fix it then take it to a gunsmith and get it fixed or return the gun to the manufacturer for repair.

    Do not shoot it again unless you like free striped clothes.

  11. jlloyd73

    jlloyd73 Active Member

    Nov 28, 2010
    Thanks to you all for the responses. For all off you that are are referring to the disconnector-trigger/sear being the are absolutely correct. I did the simple test that several of you suggested and the hammer fell on the pull and then release (It was very hairy though, the recoil would be enough to release the hammer again). All of the parts look like they are in good condition, but I think I will strip the lower and post a pic of all the parts to see if that points to the culprit. The AR is a pretty easy gun to work on and repair, so it shouldn't be a hard fix.

    Luckly I live in a very rural area and normally it is only me and a few family members shooting, so I don't think I will be needing the fancy orange jumpsuit favored by our local law enforcement.
Similar Threads
Forum Title Date
Technical Questions & Information Ar-15 in 7.62x39 Mar 2, 2016
Technical Questions & Information How to get original finish (paint) off of AR-15 30 round magazines Sep 5, 2014
Technical Questions & Information 80% lower AR-15 question Mar 6, 2014
Technical Questions & Information Magpul Accessories for AR-15??? Mar 30, 2013
Technical Questions & Information ar-15 stripped lowers Dec 20, 2012