"Accidental" binary trigger on an AR-15

[DoggyDaddy]

Just took the last AR I built for it's maiden voyage to the range this morning and had something odd happen. First trigger pull, it seemed like I popped off a double shot burst. My buddy was shooting his AR too, so at first I looked over at him to see if maybe he had just happened to fire at about the same time I did. I asked him if I just had a "double tap" and he said I did. Tried a couple more times, same thing. Eventually I realized what was truly happening.

My trigger (Rise Armament drop-in trigger) was acting like a binary trigger. It would fire on the initial pull, and then again when it reset. Took the upper off to confirm and that was indeed what was happening. I took a closer look and it appeared that the entire assembly was able to "rock" front to back just a tiny bit, which I think is causing the issue. I noticed there are two tiny set screws at the rear of the assembly. Do I just need to tighten those down to solve this? I'm guessing I do, but thought I would ask INGO first.

I've always thought binary triggers were a bad idea (still do), but particularly bad when they're not supposed to be binary triggers! (Although I will admit that once I found out what it was doing, I put another mag through it and giggled a little. ) Fortunately we were the only ones at the range this morning. Despite being kind of fun, I don't want this "feature"!

 

[IndyDave1776]

Despite being kind of fun, I don't want this "feature"!

What? You mean a vacation of Club Fed doesn't appeal to you?

 

[DoggyDaddy]

What? You mean a vacation of Club Fed doesn't appeal to you?

I don't know that it would technically be illegal since it's not firing full auto, just two shot bursts, and I could control the rate of fire by simply holding the trigger back until I was ready to let the second shot go. Besides they do make binary triggers. But no, that is not a vacation I want to take at any rate!

 

[Dean C.]

YES tighten down the screws, they tension the unit inside the lower receiver. Another fun fact (and reason I like tensioned drop in units) is that this tension acts as a sort of anti-walk prevention feature making the pins much less likely to move under recoil

 

[gmcttr]

....Do I just need to tighten those down to solve this?...

May or may not solve your problem, but it will stop the movement. Manufacturer's Instructions are always a good place to start....

https://www.risearmament.com/blog/how-to-install-your-rise-armament-trigger/

"STEP 8
This step is optional if you’re using KNS pins but required if you’re using standard pins. There are two small setscrews located on the trigger system under the hammer springs. Lift or shift over each hammer spring and use a 5/64 Allen wrench to snug the setscrews to the floor of the receiver. Do not overtighten, as this will change the poundage of the trigger. This step is necessary for the weapon to function properly without KNS pins."

 

[DoggyDaddy]

YES tighten down the screws, they tension the unit inside the lower receiver. Another fun fact (and reason I like tensioned drop in units) is that this tension acts as a sort of anti-walk prevention feature making the pins much less likely to move under recoil

May or may not solve your problem, but it will stop the movement. Manufacturer's Instructions are always a good place to start....

https://www.risearmament.com/blog/how-to-install-your-rise-armament-trigger/

"STEP 8
This step is optional if you’re using KNS pins but required if you’re using standard pins. There are two small setscrews located on the trigger system under the hammer springs. Lift or shift over each hammer spring and use a 5/64 Allen wrench to snug the setscrews to the floor of the receiver. Do not overtighten, as this will change the poundage of the trigger. This step is necessary for the weapon to function properly without KNS pins."

Thanks guys, I will give it a try. I am using KNS pins by the way, and have used them in all my builds, but I guess they're not a failsafe.

 

[NKBJ]

Kinda achieved that effect when concocting jack rabbit ack-ack loads for an FN49 with 125 grainers.
My bright idea was starting low and increasing the charges until reliable functioning was obtained.
Eh, didn't quite work out as planned.
The better 2/3's was sitting off my right with the spotting scope.
She got hit with multiple 8x57 cases when the charge was adequate to function the action and grab another cartridge but not reset the sear.

The 125 grainer was really accurate though.

 

[DoggyDaddy]

Problem fixed! About a 30 second job including taking the upper off, and now it's working and trigger resetting properly.