New AR build double fire

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Dieselcamino

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Hey Guys,
Finally got out to the range today to try out my recently assembled stag arms retro rifle kit on a sporter match hbar lower (stag lower parts kit as well), a few rounds in a got a double fire, assumed it was a bump fire being new to the gun, paying closer attention to my triggering, a few rounds later i got a second one when I released the trigger, put it away for the day after that.
After searching online once i got home I tore it apart and checked the disconnecter spring and found it to be correctly installed (fat end down into the trigger)
Hammer spring is also on correctly

With the gun open holding the hammer I can cycle it and occasionally get it to drop on the release of the trigger (catching it with my hand of course)
A little puzzled as those two errors seem to be the cause in 99% of what I read
 
I've only witnessed doubles when a friend inadvertently loaded rounds with pistol primers. Shot 2-3 round bursts until I intervened. :) I have nothing else at the moment other than possibly light loads and hammer follow. good luck

M
 
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I Was firing lake city 62 grain green tip, but I'm sure ammo isn't the culprit since I can recreate the issue by hand with it opened up.
 
Dieselcamino said:
Hey Guys,
Finally got out to the range today to try out my recently assembled stag arms retro rifle kit on a sporter match hbar lower (stag lower parts kit as well), a few rounds in a got a double fire, assumed it was a bump fire being new to the gun, paying closer attention to my triggering, a few rounds later i got a second one when I released the trigger, put it away for the day after that.
After searching online once i got home I tore it apart and checked the disconnecter spring and found it to be correctly installed (fat end down into the trigger)
Hammer spring is also on correctly

With the gun open holding the hammer I can cycle it and occasionally get it to drop on the release of the trigger (catching it with my hand of course)
A little puzzled as those two errors seem to be the cause in 99% of what I read
Click to expand...

Based on your description it sounds fire control group group related. Without seeing it myself and diagnosing it, it makes it hard to diagnose the specific part. It's likely disconnector related but it could be the sear to hammer notch engagement surface. I'd send the whole fire control set back to the vendor and have them send a replacement.
 
Is your disconnector somehow wedged in? Check it for free movement before you do a whole lot. If it’s dragging or wedging in as the hammer passes during cycle then it can “miss” the hammer and you will see hammer follow and stringing.

Best bet is to pull the fire control group out. Make sure you use the same pin to assemble the disconnector and trigger together outside of the rifle. It can be that the disconnector is dragging the trigger, or it can be tight to the pin. While everything is out check it for burrs, scratches, chips etc. something is out of whack.

Take pictures and post as well. Maybe the seasoned eyeballs will spot the issue.

Check the safety for scratches too. Unlikely but the safety can drag the hammer and cause trouble. I had an out of spec safety that caused dangerous conditions.
 
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The disconector moves freely (with given spring resistance) up and down, I took everything apart cleaned it all and re-assemebled/oiled, still get a fire-on-release maybe once every ten trigger pulls.
Safety looks clean minus some scratching where the detent sits (assuming that's normal)

Think I will give stag a call in the morning see if they have had similar issues.
 
Walkalong said:
Ditch the trigger group and buy a quality replacement.
Click to expand...

There is absolutely nothing wrong with a in-spec standard trigger group. His clearly is out of spec. I have no doubt Stag will take care of it. The last thing on earth they want the potential liability that they could resolve with a very low cost replacement part.
 
Sounds like you did your due diligence on troubleshooting. Call manufacturer and explain as clearly as possible what you have found. They may send parts, but more likely they will want the gun to troubleshoot it and repair it themselves. If they want the gun back send it to them exactly as you got it. Take off anything you have added and put back anything you removed. It may be the fire control group out of spec, it could potentially be a lower out of spec.
 
Yeah. Sounds like out of spec trigger group. Probably by only a couple thousandths, but if you dont replace it, the problem is likely to get worse as the parts break in and the distance between the disconnector and the primary sear open up as parts smooth. Thats my take on it, anyway.
 
Thanks guys I appreciate the help, not sure if they will take the whole firearm back since I only purchased the retro rifle kit, not the assembled firearm, had to use a preban lower being from CT (ironically 25 min. From stag arms.)
 
The only other thing i might say is, maybe before shipping the parts back, if you have a friend with an AR with a known good trigger, see if they might be willing to swap trigger groups and retest.

Only because the other possibility i could conceive of would be pivot pins drilled wrong in the lower. That could change the relationship of the sear and disconnector slightly, too, and mean a new trigger group won't fix it.

But i still think the FCG parts are the primary suspect.
 
A lot of good advice here. I have seen this before and it boils down to two locations. Either the fire control group, as discussed earlier, or it is often the bolt carrier.

I have seen a bolt carrier, even one in spec, be machined a bit to high, with not enough material to fully reset the trigger back to the sear, resulting in the trigger slipping off the sear (instead of being locked back for the next shot) causing a double fire.

Replace the bolt carrier is what I'd do first.
 
Only reason I'm leaning towards the fcg is the fact that I can recreate the issue with the gun opened up resetting the hammer by hand,
 
If it's doubling on the release, then it's not the BCG. It's the FCG.

When the BCG is machined incorrectly, the hammer isn't pushed far enough to engage the disconnector, so it would NOT double upon release. So this problem is NOT an out of spec BCG. Out of spec BCG's will let the hammer follow the carrier, VERY VERY rarely will these snag enough to double, they usually just follow. Doubling on release is indication it's snagging the disconnector just fine, and NOT a problem with the BCG.

What's happening here - the disconnector is snagging the hammer, but it's insufficiently long in the tooth, so it's not hanging on long enough during trigger reset to let the trigger catch the sear. This seems like a problem, since you can't add length to the disconnector tooth, but it's actually VERY simple to fix. 15min job - pull the upper, stick a foam ear plug in front of the hammer, then start taking licks with a file on the bottom side of the front spur of the disconnector and she'll be running just fine. No customer service, no wasted time...

All you're trying to do is allow enough disconnector travel to let the trigger raise to catch the sear as the disconnector releases the hammer. Right now, it's letting go before the trigger has reset far enough to catch. Take a little off of the underside of the disconnector "toe" and all will be well.

Disconnectors and mil-spec triggers are cheap enough, no real reason to not buy new, but personally, I'd have done the proper disconnector test before I ever fired a shot, and would have filed the tip of the disconnector to make it run right, before it ever got to the field.
 
varminterror- I think you have hit the nail on the head, with some more online digging i found a YouTube video that explains exactly what you described, (only his issue occurred after a home/hack trigger job)
- I did run a few Disconector tests on it, but the problem is maybe 1/10th of the time so I missed it before it made it to the range.



Jackal - I appreciate it, I will take you up on the offer if stag won't replace them, (would like to know how they stand behind their products)
 
ColoradoMinuteMan said:
There is absolutely nothing wrong with a in-spec standard trigger group. His clearly is out of spec. I have no doubt Stag will take care of it. The last thing on earth they want the potential liability that they could resolve with a very low cost replacement part.
Click to expand...
Yes, Stag should make it right, and yes, mil spec triggers are fine, assuming they function properly, but me, I would just upgrade and not worry with it. If money is an/the issue (Money is money, I get it.), then worry Stag until they make it right, and I am sure they will.
 
Jackal said:
Send me $4 Paypal to cover shipping and I will send you a milspec FCG for free, I have extras.
Click to expand...
Very generous Jackal, I bet there are a lot of mil spec take off trigger groups laying around out there where folks have upgraded. :)
 
Walkalong said:
Yes, Stag should make it right, and yes, mil spec triggers are fine, assuming they function properly, but me, I would just upgrade and not worry with it. If money is an/the issue (Money is money, I get it.), then worry Stag until they make it right, and I am sure they will.
Click to expand...

I get it, but why even order an LPK with a FCG if you aren't going to use it. Personally I just order LPK minus FCG if I can't get an LPK with the upgraded trigger I'm looking for. If I paid for an LPK with a FCG and it didn't work I'd want to have it replaced and ensure that all of the parts I purchased were in spec and working, even if I was going to put them in a bag in my parts box. You can always upgrade the trigger later, but why not take some extra time to get what you purchased functioning. That way down the road ifnhe upgrades he has a set of spares in case he he needs them.
 
Varminterror said:
If it's doubling on the release, then it's not the BCG. It's the FCG.

When the BCG is machined incorrectly, the hammer isn't pushed far enough to engage the disconnector, so it would NOT double upon release. So this problem is NOT an out of spec BCG. Out of spec BCG's will let the hammer follow the carrier, VERY VERY rarely will these snag enough to double, they usually just follow. Doubling on release is indication it's snagging the disconnector just fine, and NOT a problem with the BCG.

What's happening here - the disconnector is snagging the hammer, but it's insufficiently long in the tooth, so it's not hanging on long enough during trigger reset to let the trigger catch the sear. This seems like a problem, since you can't add length to the disconnector tooth, but it's actually VERY simple to fix. 15min job - pull the upper, stick a foam ear plug in front of the hammer, then start taking licks with a file on the bottom side of the front spur of the disconnector and she'll be running just fine. No customer service, no wasted time...

All you're trying to do is allow enough disconnector travel to let the trigger raise to catch the sear as the disconnector releases the hammer. Right now, it's letting go before the trigger has reset far enough to catch. Take a little off of the underside of the disconnector "toe" and all will be well.

Disconnectors and mil-spec triggers are cheap enough, no real reason to not buy new, but personally, I'd have done the proper disconnector test before I ever fired a shot, and would have filed the tip of the disconnector to make it run right, before it ever got to the field.
Click to expand...

I completely agree with your diagnosis, however, I've just never been a fan of filing fire control parts unless you really know what you're doing. I know many people do it successfully and have no issues but for the small cost of a replacement part like a disconnect or, I'd just replace it. The FCG is the most critical safety mechanisms in a firearm. When you file them down you remove the case hardening and that metal is all the sudden software and more susceptible to wear. I'd rather leave that undisturbed. Anything more that a mild polish is too much in my opinion.
 
@ColoradoMinuteMan - if you understand the workings of the disconnector and the dimensional correction I described above, you would understand no hardening would be of any benefit for the relationship between the trigger and disconnector. It’s a dead stop position with ample tolerance margin, not a surface exposed to high wear or impact. And you’re assuming the disconnector is surface hardened - in my experience in hundreds of trigger jobs on AR’s, even if the disconnector is SUPPOSED to be hardened, most “mil-spec” disconnectors sure aren’t...

Not every component in the FCG needs surface hardened, and not every contact surface is a critical dimension for safety. Your statement is an overly cautious lack of understanding.
 
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