You all know the story, boy sees gun, boy lurks here for a few months, boy buys m&a 16" mid-lenght parts kit, boy puts gun together according to this site (thanks by the way).  Boy likes the fit and finish and is stoked to finally have an AR of his very own.

Now the down side, boy takes the black beauty to the range, pulls the trigger and, "bang, bang, bang".  My first thought is hat because I don't know what the hell I'm gonna do with a "full auto"...Uh, Oh.  so now the trigger won't reset and the chamber is loaded.  Drop mag, clear chamber on a live round with a small dimple in the primer, check gun over, re-insert mag, chamber a round, pull trigger and again, full auto until the trigger won't reset, wash, rinse repeat.  I can stop the auto by letting go of the trigger but it usually goes until it stops on it's own.  So, hoping to avoid the hefty $10,000 fine for owning a full auto illegally, I stop after my two magazines, remove the upper from the lower, put the lock on the trigger anyway, leave the range like nothing happened (and like I knew it was that way and legally owned the gun) and home I go.  

I've emailed m&a parts already but, since it's the weekend, I won't hear back until Monday.  I guess I'm looking to see if this is my fault.  Did I put the lower parts together wrong?  It is the upper?  If I put it together wrong how can I fix it?  I used a Rock River Lower receiver and one of the reasons I went with m&a is their mid-lenght kits are also made by RRA and sure enough...there's the little logo on the upper.  I don't know enough about these babies yet to try to fix this without help so if you would all be so kind...

Thanks.

Sounds like the disconnector is not catching the hammer when the action cycles.
Take the lower and while holding the trigger pull back on the hammer, the disconnector should catch and hold the hammer until you release the trigger. If it doesn't then you will have to file some material off the front bottom of the disconnector until it does.

ar15.com/forums/topic.html?b=3&f=66&t=240125
Check the troubledhooting section. The link above has some info part way down the page on how to check a lowers function. Also I would check the disconnector spring for proper installation and free movement of the disconnector.

Recheck your disconnector, spring, and trigger assembly, and make sure it is in correctly.  Often times people will put the spring in with the thin side down, and that will get you nothing but problems.  




Take a look at these pics and I hope they help.

edited

I almost installed my spring wrong on my first build however I caught my self after reading the guides here.

Thanks everyone for your help...sure enough, spring in wrong way.  All better now.  BAck to the range!

THanks again.

The pic in "assemble your lower" guide here is a little misleading when it comes to that disconnector spring. Not that I would ever put mine in upside down on my first build or anything...

Shouldn't the notch on the hammer snag on the firing pin as the bolt goes forward? Unless you have a full auto bolt without the cutout...
Regards, Ray

Changing the Fire Control Group (Hammer, Trigger, Disconnector) & all their associated springs should solve the problem; One of the above parts is most likely worn or out of spec.
It would be nice if you can take some photos of the FCG parts & post them so us board members can take a look see!
 

He fixed it guys, spring was in upside down.

That's all it takes to go full auto is a spring upside down? Not worth it, don't want to meet Bubba....

You know, I once had this set of mostly used GI trigger parts that eventually, reliably, went bang once each time I pulled the trigger, and also went bang once each time I released the trigger.  I'll assume the disconnector wasn't catching upon releasing the trigger.

This was fun and all until the day I had to stop shooting at a USPSA match on an odd numbered round and explain to the RO why I could not remove my finger from the trigger until after I dropped the mag and pulled back the bolt to eject the live round.

Hmm, I don't think that meets the letter of the BATFE's description of a full-auto as it indeed only goes bang once when the trigger is pulled.  And of course once when it is released.

I replaced those well-used parts with all brand new parts and kept the old parts, just in case.  But I have since lost those parts to a house fire.

Oh well, it was fun while it lasted as I could really empty 30rd mags twice as fast as the next guy.  But getting a knock at the door from your not-so-friendly neighborhood BATFE agent doesn't exactly sound like my idea of an evening well spent either.

Quoted: He fixed it guys, spring was in upside down.

What spring?

Quoted: Quoted: He fixed it guys, spring was in upside down. What spring?

My boss at the ATF won't let me say. I made the same mistake when I assembled my first lower, had to go change my underwear.

Quoted: Quoted: He fixed it guys, spring was in upside down. What spring?

Disconnector spring.

Glad things worked out for you, but ALWAYS-ALWAYS-ALWAYS when firing a new weapon for the first time, never fill the magazine!! Start out wit at most 2 or 3 rounds and make sure everything functions properly

Quoted: He fixed it guys, spring was in upside down.

upside down disc. spring = whoa!

Quoted: I replaced those well-used parts with all brand new parts and kept the old parts, just in case.  But I have since lost those parts to a house fire.

Yeah, those ATF guys don't fuck around.  What set fire to the house, smoke or CS grenade?

So DON'T put the smaller side of the disconnector spring into well of the trigger? I just took a look at Duncan Long's book, and he writes to put the smaller side down.

Quoted: So DON'T put the smaller side of the disconnector spring into well of the trigger? I just took a look at Duncan Long's book, and he writes to put the smaller side down.

When I was young & Inexperienced at building AR15s, I installed this spring both ways & Never had a gun go full auto Strange, Very very strange

Check your firing pin. Someone might have filed it down a bit when you weren't looking.

sounds like a newbie story kinda,  dunno never ran into this,  I have run into my M1 garand sitting in the gun safe while at basic training and come home to shoot it let the bolt go and the gun emptied because the firing pin was stuck.  I figure the grease stuff must have dried out with the hammer sitting against the pin.   Anyway  I had a Colt break a disconector and all that did was completely made the rifle not function. The hammer got hung between the front of the firing pin thingy and the bolt.  was a bitch to get the rifle apart.  The little hook broke clean off and that cuased it.


I think you should look into slamfire,   check your Firing pin, and the bolt for a shard or something left over from machining