Just got back from the range.  Have a flattop match style AR and had a problem with it doubling today.  I cleaned it last time I used it but nonetheless I cleaned it again at the range.  There was some carbon inside the bolt carrier that I missed before but got it all out and it was still doubling about every 3rd shot.  Loaded only 2 rounds in for 10 consecutive shots and it worked fine.  Loaded 5 rounds and it doubled.  Loaded single shot for 50 more rounds and worked flawlessly (never went off because of "slamfire" as I was thinking it would), this leads me to believe that it might be a problem in the lower.  I don't take it apart and clean the lower much because it doesn't seem to get very dirty down there.  Could this be the problem??  Thanks for the help and let me know if there is any other info I can give that might help the diagnosis.

Damian

I would suggest you are wearing things out by cleaning the rifle so damn, much.

Anyway it's not carbon, build up or any other dirt related cause. Either your semi auto disconnector spring is missing/weak or the hook on the disconnector is worn or the hook on the back of the hammer for the disconnector is worn. Do the following test.

Take the upper off the lower. Cock the hammer while the trigger is pulled and held. The hammer is now held back by the disconnector and not the trigger sear.  With your other hand grab the hammer and jiggle/pull forward on it. You will most likely see that it can be pulled/slipped off the disconnector.

This is what is happening replace worn parts as needed.

Have you polished/ stoned/ dremeled and parts lately?

If so, replace those parts.  If not, you may as well gut your lower and replace everything.  You could go piece meal replacing parts, but you may as well do it all.

Have you tried function checking your rifle?  When you let the trigger out on your check, do it verrrrry slowly, it will probably slip and drop the hammer again.

As posted above, its time for replacement parts.  Cleaning shouldn't have much to do with it.  

A quick cure might be to check the spring and see if it is still present.

It definately sounds like a disconnector problem, but there is another test.  Unload and open up the receivers.  Hold the hammer, press the trigger, and allow the hammer to go forward under control.  Don't just snap it.  DON'T let the trigger go.  Keep it trapped to the rear.  Then manually cock the hammer.  It should be caught by the disconnector.  Now, release the trigger.  If the hammer fails to be caught by the trigger, than your engagement is off.  Either at the disconnector/hammer engagement, or the hammer/trigger.

What you are likely getting is one shot when you press the trigger and one when you release it.  If you press and release pretty quickly, it will seem like it's doubling.

very good advise for anyone wanting to make sure their AR is working properly, this should be TACKEd on the BUILD site on here.

Agreed, and that is what a proper military function check of your rifle does, but without having to open it and catch the hammer.

The check is simple and should be done every time you clean your weapon.

I was having a similiar problem recently with my Colt AR-15.  My AR would fire when the trigger was pulled and again whent he trigger was released.  I swapped three complete sets of lower receiver parts trhough the gun and still it still double tapped.  I then ordered a complete set of lower receiver springs from Bushmaster.  A new hammer spring cleared up my problem.


Here's a link to a related discussion:

[url]http://www.ar15.com/forums/topic.html?b=3&f=66&t=163258&w=searchPop[/url]

Thanks for the replies guys.  I have tried holding the hammer every which way, releasing, and all of the suggestions.  Can't get it to fail any of those tests.  I have looked all over the site for the "Military Function Test" cause I know I have seen it posted but can't find it now.  I noticed a little bit of uneven wear on the hammer where the bolt rubs but other than that everything looks and runs Kosher.  somebody post the military function test so I can try that.  Thanks, D

SSSHHHHHHHHHHHHHHHHHHHHHH, don't tell everybody!

Could your trigger be bouncing on that nice light target trigger?

I've done that.

My bushmaster was doing the same thing at the range and I discovered that the trigger piviot pin was working its way out of the lower.  I tapped it back in and have not had any troubles since then..

-Matt

i had a problem with my ar after i filed the catch on the hammer to make a shorter smoother trigger pull, the pull was wonderfull after but i kept getting a double shot when my trigger pull was slow but when i was pullin fast no problem. to make a long story short i replaced the hammer and that fixed it

Gee, I wish my Bushie would double. keeps you on your toes.

My [url=http://world.guns.ru/assault/as55-e.htm]SAR80[/url] rifle does also double fire every now and then. I noticed the problems after I changed the original milspec springs to lightened ones. With the lighter springs it was easier to release the trigger very slowly and when it was done in this manner the disconnector´s hook released the hammer too early for the trigger to catch it. My rifle had been modificated from full auto parts to work semiauto only but it seems that the work wasn´t done/tested properly.

Usually the rifle double fired when the shooter was taking very difficult shots and had to concentrate on the triggercontrol carefully. One time my brother managed to do 6 round burst in a competition when shootin a plate at 110 yards. With the light trigger and effective muzzle brake the SAR80´s heavy bolt carrier made the gun move back and forth and that caused the burst. At least that is what I believe caused the burst. It was too bad that the double fires never happened when it had been convenient e.g. when shooting close targets.

PS. The burst scared my young brother quite a bit. Unfortunately the burst didn´t take that plate down allthough all the six bullets hit very close by thanks to the Miculeck comp. The range officer saw his trigger finger move so he was amazed how quickly my brother was shooting. [:D]

Don't neglect the firing pin.  Is the firing pin channel free of gunk?  Can the firing pin move back and forth freely?  It could be causing an intermittent slamfire but more than likely the problem is with your lower.  

I had a similar problem with my Olympic 9mm AR, and I finally fixed it by swapping out my CAR stock for an A2 stock.  I guess the CAR buffer and spring were just imparting too much energy to the system, jarring something loose.

[url=http://www.ar15.com/content/docs/functionCheck/]function check[/url]

I had the same problem iin the past, check to make sure your pins are in place.

Thanks Phil.  Pins seem to be fine as well.  I will try to get it out this weekend and run some through it.  Will let you know how it goes.

D.

OK guys 120 rounds without a hitch.  I think it was the pins loose as this was really the only thing that I fixed before trying it out again.  I am going to replace the disconnector spring anyway, just so happened it started working before I had done that.  I think that when the pins work their way out a little, things are lined up as well.  Thanks for everyones help.  This was some really good info in this thread.

Damian