full auto problem

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newgunmike

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ok, so today i went to test out my ar and i had a few 2rd bursts. now i didnt mod anything and i dont want full auto, i put a brand new hammer in my ar a week ago and i did maybe 100 or so function test prior to the outing. nothing was wrong and i never had a jam with snap caps. i fired 60rd and maybe had 6 or seven bursts, after checking it over, everything was fine and i did a function test and noting was wrong. so i went to do a little target practice and fired another 60rds without a single jam or burst. what im thinking is that i might have been bump firing it by accident the first time, because the first 60rds i was somewhat rapid firing and the second time i was firing slow. could it be that i might have been bump firing or do you guys think it was something else.
also i have a good muzzle brake on my ar and it eliminates almost all the recoil, not sure if that might have something to do with it.
thanks.
 
Bump firing, or ammo with soft primers.

Doubles are pretty common with reloads and smashed in primers seated to hard..

rc
 
i was using federal value pack from walmart, do you think those have soft primers.
 
Federal primers are known to be more sensitive then other brands.
However, they should know what they are doing.

Check some that have been chambered semi-auto, but not fired, and see if they have deeper then normal firing pin dings on them from the bolt slamming foreword.

rc
 
"Put a brand new hammer in last week" That's where I'd start looking. And why the new hammer? What is the condition of the sear? Occasional and random burst firing is often disconnector timing related, which takes us right back to hammer and sear relationships. I'd suspect ammo last on that list. In who knows how many thousands of rounds of various handloads and all sorts of commercial and mil I've NEVER had an actual slam fire either in the firing cycle or dropping the bolt on a round. I have seen disconnector issues emerge from wear or unadjusted parts changes, and the result is exactly what you describe.
 
agree with bwb. put your old fire control group back in and see if it happens. my guess is no.
 
well the reason i switched hammers is because the last one would not engage the disconnector after cycling the bolt and holding down the hammer, but when i put the new one in if worked fine. i think maybe i'll buy a new disconnector and see if that fixes the problem. i will need to wait till next saturday, however the last 60rds had no problems. maybe since it was a new rifle and i hadn't shot a ar in over a year i was pulling the trigger to lightly.
also the disconnector looks new as well as the trigger but better safe then sorry.
 
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ok, i just ordered a trigger, disconnector, and disconnector spring from del-ton because thats where i bought the hammer so problem solved, i think. is ther anything else that could be causing a problem.

i should have changed the entire fcg when i bought the rifle because it did look as if the hammer was either heavily used or modified.
 
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Your are aware there is a man in jail right now for having had this kind of thing happening with his ar? The gun was screwed up, not modified. Oh and you can not trust the liars at the BATFE.
 
yeah, i remembered that story when the first burst happened which is why i want to make sure i get if fixed asap. fortunately it happened on private land.
 
You don't need to spend any money to fix the problem.
Simply remove the disconector and grind about .015" off the underside of the front foot. That will fix your problem.

Tony Rumore
Tromix Corp
 
Two things to check either now or when you install the new parts:

1) With the upper off of the lower, hold the trigger back and cock the hammer. Make sure the disconnector engages the hammer hook - I like at least .030 of engagement.

2) Place your thumb in front of the hammer to block it and slowly release the trigger. The sear should catch the hammer, again I like about .030 min sear engagement, when the disconnector lets the hammer go.

If the FCG fails either of these tests you have a problem.

#1 can be fixed by removing material from the "foot" of the disconnector to let it come further forward. If after timing the disconnector #2 persists it means something is seriously out of spec and you need a gunsmith.
 
well i just removed some material from the foot of the disconnector and it grabs better and seems safer, however i did the test you described about 10 times before and after i removed the material and it worked flawlessly both before and after the mod.
one thing i did notice is that before the mod. i could release the hammer while holding the trigger down if i push up on the hammer with a screwdriver with a little force.after the mod it takes alot more force and the hammer will not release, so it seems to be better than before.
 
You can remove material from the "foot" of the disconnector until it just barely clears the hammer as you let the trigger go forward. The second issue with the disconnector is that if it can come too far forward it will give you a two stage trigger. Not necessarily a bad thing.
 
It's a disconnector issue. I had the same thing happen once with an AR15 fire control group that I was using on a homebuild gun project. I had ground on the disconnector a little because my trigger and hammer pin holes were slightly off. But I ended up getting 2 round "bursts" instead.

Don't worry too much about getting into trouble, though. In fact, what is happening is not a "burst" but a controlled set of two rounds being fired.

One round is fired when you pull the trigger. The disconnector then grabs the hammer. However, when you release the trigger, it has not yet caught the hammer on the front of the trigger, so the disconnector releases the hammer and it hits the firing pin again. Since the trigger has been released, the hammer catches on the trigger this time. The result, especially if you release the trigger quickly after each shot is a perceived "two round burst."

What's actually happening is that you've essentially got a trigger that fires on pull AND release. That's not illegal. A machinegun fires more than once with each "action" of the trigger. A pull is one action and a release is another action. The BATFE has issued letters to that effect. So you've done nothing illegal, even if you did it intentionally.

It's just not a very useful functionality to have in a rifle, since you can't "switch" to it from single fire because it's a disconnector malfunction. So it's best to fix it.

Aaron
 
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so in order to fix that problem i need to grind down a little bit of the disconnector foot, because thats what i did.
 
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