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9/22/2017 12:11:25 AM
Posted: 8/7/2005 12:28:14 PM EDT
Here is the equipment we are talking about...

Colt MT lower, bone stock.
Bushy M4 profile upper w/ Bushy bolt and bolt carrier....bone stock.
Various 30 rnd mags, some new, some used, some very used...have never had issues with any of these mags before.

I shoot a pretty even mix of XM193, Q3131A, Wolf 62gr in .223Rem
Last week I picked up some M855...I had never shot this stuff before.

The place I was at yesterday is very strict about no rapid-fire (most a hunters hangout),
so I was pretty self conscious about taking a few breaths and a good few seconds between shots.
I was just taking my time, seated at a bench, going through 30 rnd mags.

I started yesterday with the M855. About 100 rounds in, maybe half way through a mag,
I fired a shot and to my surprise, 3 or 4 went off in maybe 1/2 a second.

That freaked me about a bit, since it has never happened before, so I pulled the mag, ejected the live round, pulled the takedown pin and inspected the trigger group and bolt to see if anything was obviously out of whack.....nothing....everything looked fine.

I loaded up again and went through a few more shots....no problems.
I finished up the M855 (one more mag), then went between xm193, some American Eagle loaded in Lake City brass in .223Rem, and then some wolf 62gr.

The issue never happened again.
I took everything apart today to inspect and found nothing wrong...the bolt, carrier, extractor, trigger group....everything appear fine.

I remember a thread about this a year or more ago....but the guy was shooting underpowered ammo and thought that his bolt carrier wasnt fully returning to the rear, and not engaging the catch on the hammer, which would then fall on the next round as it was loaded into the chamber. I cant imagine this was the problem shooting decent quality M855 5.56 ammo.

I dont think i cooked them off because I was just getting started for the day...gun just wasnt that hot (does a semt ever even get hot enough to cook off a primer?)

Any thoughts?

In looking at the trigger group, the only thing that I could come up with was, when I pull the trigger, (and keep it pulled fully to the rear through the cycle) and the disconnecter releases the hammer to go forward....the carrier will then return the hammer to battery and catch but seat on the disconnector until I release the trigger forward with my finger....I found that if i very slowly released the trigger forward, rather than sit on the disconnector retained by the sear ridge, the hammer would actually drop if I moved very slowly through the motion. I cant tell if this is normal, of if something is out of whack.

In all the times I have fired with live ammo, not once has releasing the trigger after a shot caused the hammer to fall on the chambered round. It seems a bit sensitive when manually working through the cycle by hand (just using my thumb to mimmick the carriers job with the upper removed)....any thoughts?

I have a gone several thousand rounds without an issue, and I put probably 300-400 downrange after this happened yesterday without any problems whatsoever.

I figure I will continue to shoot it and see if the problem creeps up again...if it does, I am leaning toward replacing the trigger group, as it seems like the weak link here.

Has this happened to you?
Any suggestions?

Link Posted: 8/7/2005 12:36:40 PM EDT

Originally Posted By macro:
Any suggestions?

Yes, check the FAQs in the Troubleshooting Forum if you have not already done so.
Link Posted: 8/7/2005 1:06:54 PM EDT
Just looked through the TS threads...found one thing that sounds similar....although not exactly...but it still leads me toward the same conclusion.....trigger group issue.

I am also wondering if this could simply be an ammo thing.
I had never fired M855 before yesterday, and only had the issue that one time, during a string of the 855. No problems with the other ammo.

My leading theory is that is was just an anomoly of having the trigger pulled to the rear at the exact position to make the trigger group the most suseptible to the 'bumpfire' affect.

I will take the rifle out with a bunch of ammo next chance I get and see if I can duplicate the result using varying pressure on the trigger. As cool as it felt, I dont like the idea that I dont know when a burst is coming. Sure would be a cool thing to be able to do on demand....but for now, I just want it not to happen again, at least not unless its predictable.

Link Posted: 8/7/2005 1:07:12 PM EDT
It could have been a slam-fire. I got one with my Garand one time, it's pretty scary. I'm not sure what caused it, but my Garand hasen't done it again. It might just have been a bad round out of the mix.
Link Posted: 8/7/2005 1:35:46 PM EDT
[Last Edit: 8/7/2005 1:38:17 PM EDT by Ironhandjohn]
My daughter's old SP-1 did something similar when we first bought it.... I got a good deal on it at a gun show because the seller said there was a jamming problem with it. It didn't jam, it would fire bursts with no warning.

We changed out the FCG with new parts from CMMG, and the problem never surfaced again. A friend who's forgotten more about AR's than I'll know inspected the parts that we pulled out of the rifle. The rear of the hammer was rounded off on one side, with evidence of filing or grinding on the part. We suspected some "bubba" gunsmith was trying to make it an unregistered F/A, made the rifle unreliable and then dumped it off on some poor slob(me...).

We've since fired over 8,500 rounds, ALL semi-auto, by the way, most of it Wolf, in the last 3 years. A new extractor( was it age or Wolf that killed it??) is the only thing we've done to the rifle in since we bought it, other than the FCG.
Link Posted: 8/7/2005 2:09:19 PM EDT
It is possible that it was self induced. You might have kept your finger too hard on the trigger after the rifle went off, essentially doing a bump fire.

I've seen it happen with over/under shotguns with nice, crisp triggers. The shooter will rip the first barrel, and the gun will shoot the second barrel almost immediately. Often it's because the shooter doesn't let up all the way on the trigger and recoil takes care of the rest.

My bet is you bump fired it accidentally.

Did the old geezers go range Nazi on you?
Link Posted: 8/7/2005 2:30:05 PM EDT

Originally Posted By SWO_daddy:

Did the old geezers go range Nazi on you?

If you only knew this old geezer in particular
Suprizingly, i wasnt booted from the range...no one said a thing.
I hid the situation well, and the there were a lot of people on the firing line, so from a distance it might not have gotten noticed. (he would have probably blamed the kids with the AK a few booths down before they questioned a middle 30's guy and his dad.

I was thinking that it might be the ol' bumpfire thing as well. The trigger on my AR is fairly heavy, but extremely crisp.....very very little play. I left it heavy as this is not a bench rifle, but I took the play out of it. The rifle has been extremely reliable for the last 4k-5k rounds, and I am hoping this was just some weird one time thing. Maybe the M855 recoil was just different enough that my usual routine affected it in this way.

Whatever it was, rapid fire was pretty cool for the 1 second I enjoyed it
Link Posted: 8/7/2005 3:06:03 PM EDT
Yep, had the problem with my Bushmaster A2-20". Started out as a 2rnd burst, then eventually 3 then finally 4. It was a FCG problem, I think the hammer was specific culprit. I switched disconnectors, same problem. Sent it back to Bushy, they did same, and still did it. Final shipment back to Bushmaster was a whole new FCG and problem gone. The hammer looked horrible( looked used to be honest) on the surfaces where it engages with the trigger. Failed the function tests every time. But problem was fixed, 1500 rnds now and still performs flawlessly, and eats whatever ammo I feed it.
Link Posted: 8/7/2005 3:14:09 PM EDT
yeah, when my disco failed. cut loose with a 7 round burst whoa!!

Repalced it and never had a problem since
Link Posted: 8/7/2005 4:06:12 PM EDT
No offense but theres NO SUCH Thing as a semi auto going full auto or burst "for no reason". Theres a REASON and you NEED to find it. I know Im not help here I wish I had something to tell you that would help.
Link Posted: 8/7/2005 4:13:39 PM EDT
Link Posted: 8/7/2005 4:16:55 PM EDT
Check the engagement surface of your trigger. Most likely it will be worn. You will only need to replace the trigger.
Link Posted: 8/7/2005 4:35:50 PM EDT
Accidental bump fire..
Link Posted: 8/7/2005 4:51:15 PM EDT
Chances are the either the front hook of the disconnector, or the shelf of the trigger that it catches on, ir both, are worn. They'l engage, but mot fully, so the slam forward of the bolt/carrier assy, knocks them off. The problem may not have surfaced earlier w/the ammo you've been using, and shown up w/the new stuff because of a different recoil impulse cycle w/the new ammo. Or it just might have been that that it was time for the problem to surface.

Either way, something is out of whack and needs fixin'
Link Posted: 8/7/2005 4:57:20 PM EDT
That happened yesterday at our local 3-gun match. A guy had his AR do three round bursts twice during his course of fire. Freaked him out but he kept his cool and finished his run. When he was finished we all asked him what happened. He said he had changed part of his FCG the night before. In specific the disconnector. I highly doubt you bump fired and if you held the trigger back hard that wouldn't do anything unless your disconnector was not working properly. After all that is what that part does (keeping your AR from going full auto if you hold the trigger back)

Just my .02
Link Posted: 8/7/2005 6:18:56 PM EDT
Link Posted: 8/8/2005 6:06:15 AM EDT
mine did it, exact same thing. I replaced the hammer and disconnetor, and it fixed the problem. The rifle had a ton of rounds through it, around 20k and I had already replaced a shot out barrel.
this should fix your problem. mine did it when i reset the trigger only. If i slapped the trigger, it would not happen. but if i "pinned" the trigger to the rear and let it reset it would go apeshit.
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