Has anyone had their rifle with MBT go auto on them?  I had it happen twice today, once while I was shooting and once while another instructor was shooting.  I loaded 5 rounds into a pmag and had a two round burst on rounds 4 and 5.  My co-worker had a full mag and it happened about halfway through his mag.  I thought it was a 2 round burst, he thought it was a 3.  We attempted to get it to go auto again and could not.  We didn't incorporate rifles at our monthly range days so I didn't have an excuse to shoot PD rounds, so my personal stash in my unit was limited so I didn't get a chance to keep testing.  The trigger has roughly 150 rounds on it, with about 100 being shot today.  There are no broken trigger/disconnector springs and I don't see it having weakened/worn disconnector/disconnector springs after such little use.  It is installed correctly, trigger spring under the bar with spring legs to the front, hammer spring on the back of the hammer with spring legs towards the rear.  We are two of 4 departmental AR15/M16 armorers and cannot seem to find a problem.

The trigger is from order #306XXX that was shipped in late December, 2015.  I was also shooting my Noveske that has an MBT from order #354XXX that was shipped in late July, 2016 that had 75 rounds through it today with no problems.  

Any thoughts?

Did you use the supplied pins? Are they solidly in place? What lower did this happen on?

More than likely you should to send that back to the mother ship and get a new one.

Yes, yes, and on the LaRue lower.  It is a full LaRue build with a LTS69XX SN.

I would call the shop and swap it out. Not worth jail time over trying to figure out a problem trigger...in this day and age

Thank you for the concern, that shouldn't be an issue though since it's not modified and nothing illegal occurred to make it go auto.  It's not going to stay in the gun though and will be taken out once I'm on days off.  I'll be sending LaRue an email soon to hopefully replace it.  I have another MBT in my parts drawer I'll put it in. I was more curious if anyone else has had this happen and maybe see if Mark would chime in.  Thanks for your responses.

What ammo were you using?

Blown primer pieces, plastic bullet tips, etc. can futz things up momentarily if they fall into the trigger mechanism.

Did "milking" the trigger result in an inadvertent "bump" fire?

+1 ....  this was my first thought too.

Were you shooting it from the shoulder with a firm grip, or on a bench, or prone, etc.  ?

I had fresh Fiocchi and Federal.  Mine occurred with my Fiocchi, co-workers occurred with Federal.  The trigger area looks almost spotless.

any chance your pins were walking?

No, I did not "milk" the trigger.  Mine was fired from our picnic tables under cover with my range bag as a rest from my shoulder, co-workers in the same function, using a case of ammo as a rest from the shoulder. I've never experienced a bump fire through any of my AR's in all the years and training I've been through I can see an inadvertent bump fire happening being lazy while shooting, but that's not me nor my co-worker.  I'll send an email to LaRue today to see what they want to do.  Thanks for the responses.

OP, look at how your hammer spring is installed...are you sure it was installed correctly?

I, er, know a guy that was rushing to put a lower together and happened to put his hammer spring in backwards.  He had the exact same thing happen to him (two round bursts)...supposedly.

They are installed correctly, thanks.

your tAR and MBT went full auto.... I don't see a problem.

I'm not doubting you, however my first guess would be accidentally bump firing it. I've accidentally done this with a geissele DMR trigger that was a little too light.

Since replacing with an MBT I haven't had this issue, but I wouldn't put it in the realm of impossibility.

I'd send the trigger back just to be safe, but if it happens again I'd bet it was just you accidentally bump firing.

It took multiple popped primers to get mine to even jam up , didn't realize that batch was doing that until then.  Cleared the spent primers from the lower and swapped ammo for a steel plate whacking good time

I have had the same "bump fire"  issue with a Geissele SSA-E. If I fire it with a really firm grip it's fine, but if I'm prone or on a bench and don't have quite such a firm grip on the rifle then it can happen.

Wait...so now the ATF is going to regulate garbage as machine guns?     Don't stop at shoe strings!!!!

I had a DPMS trigger in an AR once.
The gun went auto on me. I went home and took it apart for diagnosis. The pin holding the disconnector had snapped, leaving it in an odd position.


 

Same with an SSA-E.

That's why when I shoot off the bench I pull and hold the trigger to the rear on each shot, and release to reset a second later.

I am standing by for instructions.

I sent an email the other night and waiting to hear back from LaRue.

Copy me on that email

mark (at) larue (dot) com

I used the website's "contact us" with the billing and returns.

Have you had any issues shooting it off the shoulder (not on a bench)?

Send it to me, I'll take care of it for you

No I have not.  I haven't had any issues prior to this.  Majority of the shooting I did prior to the range day was prone off my range bag with no issues.

Mark and his people have taken care of me.  Thanks again for the responses and thanks Mark for the help!  Hope it was no trouble!