View Full Version : What could make a semi fire a burst?
I witnessed a semi-auto Bushmaster go 3 round burst the other day. It fired a 3 round burst on the shooter, then as they had a moment of "wtf!?" and began to remove the gun from their shoulder and set it down...it fired off another round.
The shooter was a Marine who exercised good trigger finger discipline when I observed him (I was the RO). He swears he didn't pull the trigger and the gun fired on his own, and I'm inclined to believe him. I witnessed the gun fire the 3 round burst, and it wasn't just him shooting fast. I know the difference between someone with a fast finger vs. auto fire.
I ripped the gun open thinking the disconnector was bad...it looks almost new.
It has about 1/16"-3/32" of positive engagement with the hammer, and positively engages the sear upon reset. Nothing is chipped/ worn.
The BCG is semi, the hammer is semi, the selector is semi, the disconnector is milled to be semi, the trigger is auto style. I couldn't find ANYTHING wrong inside the gun.
I'm stumped...anyone have any idea how could something like this could happen?
I'd definitely tell that Devildog not to take it back out to shoot until it's fixed. It would suck to get hemmed up by having a "machine gun".
I'd definitely tell that Devildog not to take it back out to shoot until it's fixed. It would suck to get hemmed up by having a "machine gun".
It's a rental...and we have all kinds of paperwork when it comes to doing class 3 stuff, including the manufacturing license, IIRC.
None the less, I want to get this thing figured out, pronto.
Will check the firing pin out....don't know why I didn't think of that.
how many rounds has the weapon seen? if the firing pin checks out, i wouldn't bother trying to single out any one component.. i'd probably just go ahead and replace the whole FCG and cover all my bases
It's a rental...and we have all kinds of paperwork when it comes to doing class 3 stuff, including the manufacturing license, IIRC.
Nice :cool:
I agree with BKB and replace everything. Once one part starts others are sure to follow.
Possible unintentional bump-fire?
Make sure that you have a semi-auto selector lever and not a full-auto selector lever in the weapon. Also, check the disconnector and spring as I believe that is where your problem lies. A few things to ask yourself.
1. Who assembled the weapon and what parts were used?
2. How many rounds have been put through the weapon?
Though you say you checked already and I believe you these are the only plausible reason that I can think of.
It's a rental...and we have all kinds of paperwork when it comes to doing class 3 stuff, including the manufacturing license, IIRC.
None the less, I want to get this thing figured out, pronto.
Will check the firing pin out....don't know why I didn't think of that.
Could be worth while to check the buffer detent and buffer spring as well to make sure they are performing properly.
Possible unintentional bump-fire?
That's what I was thinking.
Ned Christiansen
04-23-09, 22:28
The hammer spring is not in right and is not detenting the trigger pin, so the trigger pin has walked out a bit, allowing the trigger to go crooked, so it can't interact with the hammer like it's supposed to, but you didn't mention any pins sticking out. So I think more likely, the disconnector is holding the hammer just enough to let the thing work semi most of the time, but it's right on the edge, so sometimes the counter-recoil is enough to jar the hammer off the disconnector. With the strigger still pulled from the previous shot, it goes bang. My guesses...... either way it's something that needs to get fixed right away.
The hammer spring is not in right and is not detenting the trigger pin, so the trigger pin has walked out a bit, allowing the trigger to go crooked, so it can't interact with the hammer like it's supposed to, but you didn't mention any pins sticking out. So I think more likely, the disconnector is holding the hammer just enough to let the thing work semi most of the time, but it's right on the edge, so sometimes the counter-recoil is enough to jar the hammer off the disconnector. With the strigger still pulled from the previous shot, it goes bang. My guesses...... either way it's something that needs to get fixed right away.
I popped it right open as soon as it happened and took a quick look. The FCG pins were both flush.
Disconnector still had 1/16" or better of engagement onto the hammer, and I could NOT get it to double in dozens of dry fires.
I could maybe get a picture of the disconnector to hammer relationship, it certainly is generous.
Make sure that you have a semi-auto selector lever and not a full-auto selector lever in the weapon. Also, check the disconnector and spring as I believe that is where your problem lies. A few things to ask yourself.
1. Who assembled the weapon and what parts were used?
2. How many rounds have been put through the weapon?
Though you say you checked already and I believe you these are the only plausible reason that I can think of.
The gun is a stock Bushy. I know the selector is semi, and the disconnector is a m16 style that had the back part milled down to sit flush with the sides of the m16 trigger I checked all of it when I ripped it open later, just to make sure no-one had swapped any parts in it. (we have drawers full of Colt m16 parts laying around, none were in this gun).
Gun has maybe 2-3k through it.
I witnessed a semi-auto Bushmaster go 3 round burst the other day. It fired a 3 round burst on the shooter, then as they had a moment of "wtf!?" and began to remove the gun from their shoulder and set it down...it fired off another round.
So it fired a 3 round burst, then fired another single round sans trigger manipulation after the burst?
Was the shooter deep into sustained rapid fire? Possibility of Cook offs?
FCG malfunction covers the possibility of a burst during normal firing, but another round firing after the cycle of operations is complete and the FCG/Bolt Carrier are static is another animal. The kinetic energy was already spent and hammers following the bolt home/slippage is unlikely.
I'd go with replacing the FCG in any case. Cheap insurance to prevent a serious problem down the road in the hands of another shooter with less muzzle awareness.
So it fired a 3 round burst, then fired another single round sans trigger manipulation after the burst?
Was the shooter deep into sustained rapid fire? Possibility of Cook offs?
FCG malfunction covers the possibility of a burst during normal firing, but another round firing after the cycle of operations is complete and the FCG/Bolt Carrier are static is another animal. The kinetic energy was already spent and hammers following the bolt home/slippage is unlikely.
I'd go with replacing the FCG in any case. Cheap insurance to prevent a serious problem down the road in the hands of another shooter with less muzzle awareness.yeah, that's what both the shooter and I both witnesses. The FCG has been replaced... Just dunno what could have caused it.
Heavy Metal
04-24-09, 15:47
I popped it right open as soon as it happened and took a quick look. The FCG pins were both flush.
Disconnector still had 1/16" or better of engagement onto the hammer, and I could NOT get it to double in dozens of dry fires.
I could maybe get a picture of the disconnector to hammer relationship, it certainly is generous.
It is more than engament trave.
How stiff is the disconnector spring?
One time I didn't realize I put .154 trigger/hammer pins in a Colt 6920...took it to the range and had 2 round bursts. I quickly figured it out and put the gun back in the case. :eek:
One time I didn't realize I put .154 trigger/hammer pins in a Colt 6920...took it to the range and had 2 round bursts. I quickly figured it out and put the gun back in the case. :eek:
LOL thats a oh CRAP!:D
It is more than engament trave.
How stiff is the disconnector spring?
Someone else ripped out the guys and replaced all of the FCG parts. When I inspected it, I could not get it to "double"...he says he got it to go once when he release the trigger super slowly.
I dunno if this could have been an un-intentional bump-fire, or the disconnecter was RIGHT at the point where it could have possibly happened.
I was just stumped by it, as I couldn't get it to double in my hands...and this isn't the first disconnector I've seen needing to get replaced on an AR.
I dunno, thanks for the help though, guys!
Ned Christiansen
04-25-09, 22:34
"Got it to go releasing the trigger super-slowly"-- that is the disconnector letting loose of the hammer before the sear is in place to catch it.
"Got it to go releasing the trigger super-slowly"-- that is the disconnector letting loose of the hammer before the sear is in place to catch it.
Yeah, I wasn't able to get it to happen, but someone else said they got it to.
I figured it had to be something like that, but being that I tried and tried and tried, to get it to do that...I ruled it out.
Thanks for the help though, much appreciated.
So it fired a 3 round burst, then fired another single round sans trigger manipulation after the burst?
Was the shooter deep into sustained rapid fire? Possibility of Cook offs?
That's exactly what I was thinking.
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