Double-tap Trigger > Build It Yourself

Posted: 7/3/2008 8:48:03 PM EDT

I recently built an AR and bought a "custom-tuned" trigger for it. I got to take it to the range today for the first time. While I was zeroing it in, every few rounds I would get an unintentional two-round burst. I wasn't riding the trigger (at least not intentionally).

Anyone have any ideas why this is happening? Did the "custom-tuning" maybe polish off a bit too much somewhere?

Posted: 7/3/2008 9:03:01 PM EDT

[#1]

Ohh, better get that fixed,

I think there's a article somewhere in here about a National Guard guy that got in trouble with the ATF for the same thing. Even though the trigger is designed for semi auto but fires more than one, some call that bad

.

As to fix the problem, you might need to post what kind of trigger and what was "custom tuned" I've seen a two stage mil-spec Colt trigger do the same and the problem was a upside down trigger spring. Go figure that one out.

David

Posted: 7/3/2008 9:09:44 PM EDT

[#2]

I've heard about the upside down springs as well, in particular though, the disconnector spring. Upside down hammer or trigger springs don't seem like they could cause that, but at the least they won't strike or reset as positively as they should. Check the stickies at the top of the forum and double/triple check your spring orientation. The disconnector spring is the least obvious, but the flared end goes into the pocket in the trigger and holds it in place.

Posted: 7/3/2008 10:02:52 PM EDT

[#3]

I've had the same issue wih one of my builds.

The disconnector spring was stuck in the compressed position, causing the disconnector to not properly engage occasionally. I had to disassemble it and tweak the spring a bit to get it working right.

Posted: 7/4/2008 1:15:53 AM EDT

[#4]

I had gotten the same problem when I sent in the trigger/hammer/disconnector for a trigger job. It's a fairly easy fix, if you know what you're doing.

If you checked your disconnector spring and it's just fine and dandy, then you might have to resort to this fix:

What you need to do is see if the problem can be intentionally induced.

What you do is this:

1. Take the upper off.
2. Cock the hammer
3. Place your thumb or a piece of cloth in front of the Hammer (do not ride it with your thumb), Pull the trigger and let the hammer fall onto your thumb. KEEP holding down the trigger.
4. While holding the trigger down, reset the hammer.
5. Now slooooowly release the trigger.

If the hammer does not reset properly, and just falls as you release the trigger, then the disconnector is releasing the hammer too soon, causing the notch on the hammer to miss the sear on the trigger. REMEMBER TO LET THE HAMMER FALL ON YOUR THUMB, not on the lower, or you'll end up with a broken bolt catch or cracked lower.

See Diagram:

This happens because on a trigger job, they basically file down the engagement surface (red line) to eliminate the creep, causing the hammer to release sooner. Whereas on a stock trigger, the hammer does not have this removed. The hammer needs a little bit of overlap to catch the sear on the trigger, before the disconnector releases the hammer. If you file this edge down too far on a trigger job, the hammer could slip past the sear, giving you a 2 shot burst.

Fix: First CHECK to see that this chamfer (the red line) was cut into your hammer notch. If it has been, then you probably had a faulty trigger job, and too much was cut out. Take a triangular (square will not work) india stone, and carefully stone this surface down, so that you increase the area of engagement, so the hammer cannot slip past the sear (green line). DO NOT STONE THE RED LINE. THIS WILL MAKE IT WORSE. you need to stone towards where the green line is, where the engagement surface is. Be very careful, and take it slow. You do not want to round it off, or stone too much off. Take a little bit at a time, until the hammer stops slipping.

If you play around with the trigger mechanism, you will see how this works.

This is the problem I had, and I suspect you're having the same problem.

**EDIT** When stoning, rest the stone into the mouth of the notch, as deep as you can go. Stone using even strokes. Don't try to change the angle, just follow the surface as it is. When looking at my half-assed paint diagram, I realized that trying to achieve a new angle would be hard to do by hand. Just stone the engagement surface only - what you're trying to do is reduce the size of that chamfer. That chamfer doesn't help engagement, if you can probably see.

Once you've felt that you've stoned enough, reinstall the hammer and run the function test again. If the hammer fails to reset, you need to stone some more. Keep going just enough so that the lower passes a proper function check. Remember to release the trigger as SLOW AS POSSIBLE.

Hope this helps. If you can't possibly bring yourself to try this, then 20 bucks will get you a new hammer...

Posted: 7/5/2008 7:23:37 PM EDT

[#5]

I just decided to remove the whole trigger assembly and return it to the vendor. This just isn't something I want to mess with or get in trouble for. Thanks for the input everyone.

Posted: 7/9/2008 1:50:47 PM EDT

[#6]

Quoted:
I just decided to remove the whole trigger assembly and return it to the vendor. This just isn't something I want to mess with or get in trouble for. Thanks for the input everyone.

Ah dammit. I wrote all that for nothing, then

Posted: 7/9/2008 2:43:34 PM EDT

[#7]

Quoted:

Quoted:
I just decided to remove the whole trigger assembly and return it to the vendor. This just isn't something I want to mess with or get in trouble for. Thanks for the input everyone.

Ah dammit. I wrote all that for nothing, then

Nonsense, it wasn't for nothing; the information is now available to others who may not be able to return/exchange their trigger assemblies.

Posted: 7/9/2008 11:42:51 PM EDT

[#8]

Quoted:

Quoted:
I just decided to remove the whole trigger assembly and return it to the vendor. This just isn't something I want to mess with or get in trouble for. Thanks for the input everyone.

Ah dammit. I wrote all that for nothing, then

Nonsense, it wasn't for nothing; the information is now available to others who may not be able to return/exchange their trigger assemblies.

Ah well, I was hoping he'd try it.

Also on a side note, if anyone notices that the problem gets progressively worse, this is because that chamfer i mentioned is striking the corner of the sear of the trigger. This causes it to round off the sear, which makes it more difficult for the trigger to properly engage. So if any of you are getting double tap problems, be sure to remedy them asap.

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