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1/25/2018 7:38:29 AM
Posted: 3/30/2006 2:51:01 AM EST
Had the 9mm shorty AR (8.5" barrel) SBR out and every magazine I put through it, around round 20-25, I got either a 3 round or 2 round burst. Could it be the trigger I am using? It is a Rock River NM trigger (pretty sure - looks just like this - www.del-ton.com/detail.aspx?ID=377

Is it possible that the 8.5 inch barrel is giving me a lot of recoil back on the bolt and possibly causing the sear to engage and not lock it when it recocks the hammer?

Should I switch to a regular trigger and just keep the NM trigger on my regular 5.56mm AR-15 with 16" barrel?
Link Posted: 3/30/2006 3:01:29 AM EST
Solution: Only load 1 round per mag.

Link Posted: 3/30/2006 3:02:58 AM EST
Sounds like the disconnector is going bad.
Link Posted: 3/30/2006 3:04:56 AM EST
Try a different FCG.
Link Posted: 3/30/2006 3:14:11 AM EST
Just don't shoot it in public until it's fixed or you may be the next John Glover
Link Posted: 3/30/2006 3:14:11 AM EST
Whatever you do, fix it fast. I'm sure the ATF would love to bust someone with an "unregistered machine gun". I've heard too many horror stories.
Link Posted: 3/30/2006 3:17:44 AM EST
I'm guessing worn disconnector.
Link Posted: 3/30/2006 3:21:29 AM EST
A broken hammer pin did this same thing to me. Push out the pin and see if it is in two pieces, or grab the hammer and see if it moves in a way it is not supposed to. Mine did the burst thing, from 2-5 rounds and went full auto for about half mag when the pin finally let go making my gun into a club.

Yes, a 9mm will fire out of battery, so you MUST get this fixed. I still have my ruptured case on a shelf in my garage.
Link Posted: 3/30/2006 3:29:51 AM EST
You may want to change out the hammer spring to a light weight one. I've had to do that to 2 bushmaster lowers for the .22 uppers. The hammer spring was to strong to let the hammer go back fully. Result, full auto. One suggestion was to use high velocity (which I was) or ultra velocity (which only let it spit them out faster). For me it was the hammer spring.
Link Posted: 3/30/2006 3:30:18 AM EST
Link Posted: 3/30/2006 3:43:34 AM EST
probably the disconnector spring...thats's what happened with mine.
I replaced the spring and problem was solved.
Link Posted: 3/30/2006 3:46:10 AM EST
I also had the hammer spring problem. The hammer spring wasn't seated properly, so the gun fired twice - once on pulling the trigger, and once on releasing the trigger. I'm telling ya, nothing will scare you like a gun firing when it shouldn't, even if it is pointed downrange!

Link Posted: 3/30/2006 3:51:49 AM EST

Originally Posted By TC6969:
Sell it on the EE and claim it worked perfectly for you.

For $15,000
Link Posted: 3/30/2006 3:53:52 AM EST
Ditto on the disconnector/spring
Link Posted: 3/30/2006 3:57:27 AM EST
The accidental 2/3 round bursts are caused by the 'timing' of the disconnector. Fix the timing and the problem should go away.

Charles the Gunsmith.
Link Posted: 3/30/2006 4:02:28 AM EST
At one time, my AR-15 fired one shot for every pull and release of the trigger...

I found out when I got to the range but, I put a few hundred rounds through it to be sure it was broken...

I replaced the disconnecter and it ran fine...
Link Posted: 3/30/2006 4:15:11 AM EST

Originally Posted By ClayP:

Originally Posted By TC6969:
Sell it on the EE and claim it worked perfectly for you.

For $15,000

Call the ATF, they'll make that problem go away.
Link Posted: 3/30/2006 4:17:08 AM EST
Seek way to make the accidental 2-3 rd bursts become accidental 30 rd bursts.

I have teh same problem with my Uzi clone. Its ALMOST fun.....

Link Posted: 3/30/2006 4:32:34 AM EST
The thing is, the gun and fire control parts only have about 200 rounds through them.

So, any suggestions on where I can get the springs pretty inexpensively? Anyone have any extras lying around?

Also, maybe it is just the gun, but I've noticed a LOT of powder markings on my spent 9mm casings.
Link Posted: 3/30/2006 4:46:53 AM EST
Move that selector from"Burst" back to "Semi".
Link Posted: 3/30/2006 5:20:14 AM EST
[Last Edit: 3/30/2006 5:22:26 AM EST by FMD]

See if it will do the "burst" thing by pressing and holding the trigger to the rear (firmly).

If it's a NM trigger, it's pobably got a nice, short, reset. I've seen an AK that has a very light two-stage (almost a "set" trigger) that will bumpfire even when shouldered, if you're light on the trigger. Essentialy, the recoil moved the gun just enough to reset, and constant light pressure on the trigger made it continue to go "bang" (i.e. the trigger didn't go back to the full-forward pos). Pressing firmly to the rear and holding results in only one shot.

Sounds kind of like what you described in the first post, and I have no doubt a shorty AR with a crisp two-stage trigger would have enough recoil to do it.
Link Posted: 3/30/2006 7:15:32 AM EST
I know of a person who purchased one of those rebuilt NG M16s (rebuilt to AR15) from Century about 10 years ago... it fired in bursts.

Yeah... I know of a person. He got rid of it pretty fast.

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