View Full Version : Multiple rounds fired with trigger pull, need to fix.
UTShooter71
08-21-20, 12:56
Hola,
Well my son in law put together an AR-15. He used a Tennessee Arms polymer lower and a generic parts kit. This was not from Tennessee Arms, not sure where. The upper was a generic, fully assembled upper (with BCG and charging handle) from PSA. At the range he put a standard (metal) AR-15 mag in. It went auto. It fired until he let off the trigger. Needless to say we bagged it until we could get home and then dismantled it. I told him I would take a look at it but was wondering where I should start. The upper ran fine on my AR-15, just to verify that. The rifle was not function checked after it was put together and before it was test fired. I would like to think that it is something in the trigger group but is there anything I should look at concerning the lower receiver itself?
Gracias
lonestardiver
08-21-20, 13:03
Possibly an issue with the disconnector allowing the hammer to follow the bolt.
Replace the hammer/trigger/disconnector.
80% lower? I assume trigger/hammer pins spacing misalignment could cause the issue.
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UTShooter71
08-21-20, 15:00
80% lower? I assume trigger/hammer pins spacing misalignment could cause the issue.
Sent from my SM-G955U using Tapatalk
No, this was one of their fully drilled ones. It has brass inserts where parts screw together (buffer tube and pistol grip). Everything went together fine but this is the first time for either of us to use a polymer lower and wanted to weed this out as the problem.
Any way to measure the fcg pin holes? Could be something is binding the hammer/disconnect.
I would look at systematically replacing fcg components. I would start with disconnect/hammer.
Have you function checked it since getting home?
In addition to the obvious parts issues possibility, blown primers can end up in the fire control group and cause problems too.
UTShooter71
08-21-20, 17:30
Have you function checked it since getting home?
In addition to the obvious parts issues possibility, blown primers can end up in the fire control group and cause problems too.
Hello,
That has not been done. To be honest my son-in-law didn't want anything that could be seen as an attempt at making an illegal gun. I took it apart for him. I am going to measure the lower and compare hole location with my rifle and then go over the parts to see if the sizes are the same, if there are any burs, cracks or something we (really I) should have noticed while putting it together. I'm hoping that it is something simple, that can be replaced in lieu of the entire lower. Although I have heard that Tennessee Arms has a good warranty and customer service.
Add pictures of the FCG. My money is on a damaged disconnector
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You don't need ammo to function check the trigger parts.
Put it back together and check it out.
You don't need ammo to function check the trigger parts.
Put it back together and check it out.
I think his son-in-law is concerned about possessing a MG, so that may be a reason for not reassembling.
I was going to suggest putting the FCG in another lower and function checking. My bet would be on the polymer lower.
You don't need ammo to function check the trigger parts.
Put it back together and check it out.
You REALLY should perform a function test before firing a new AR and after cleaning/maintenance. Always STOP if a step fails.
1. Remove all ammunition from the room, triple check rifle to ensure it is not loaded.
2. Cycle action (verifying empty chamber again) and place rifle on safe.
3. Point rifle at a safe backstop and attempt to pull trigger - hammer should NOT fall.
4. Move selector to fire, pull trigger, and hold to rear - hammer should fall.
5. Continue to hold trigger, pull charging handle fully to the rear and release to re-cock rifle.
6. Release trigger - you should hear and feel a distinct click as the trigger resets.
7. Pull trigger - hammer should fall with a distinct click.
8. Pull charging handle to rear and release, then place selector on safe.
I normally repeat steps 2-8 two additional times.
If there is NO click on step 6 or step 7 - push out rear takedown pin and "shotgun" the rifle. Note if the hammer is forward (uncocked) or to the rear (cocked).
If step 6 fails and the hammer is forward - the disconnector is not catching the hammer when the action is cycled.
If step 7 fails and the hammer is forward, the trigger's sear is not catching the hammer.
If step 6 fails and the hammer is cocked, the disconnector is not releasing the hammer.
In your shoes, I would replace the FCG with a known good set and perform a function check. If it fails, the lower is suspect. If it passes, I would correctly install the old set and re-test. If it still fails the function check - dispose of the FCG and replace it. FCGs are cheap - I don't swap individual pieces attempting to fix them.
BTW - it's not easy for an AR to fail in a manner that produces a full auto rifle.
Andy
Make sure the disconnector spring is installed. This is most likely an issue with the disconnector. As another member stated, it’s allowing the hammer to follow the bolt. If everything checks out with the fire control group, it could possibly be the spacing of the hammer/trigger retaining pin holes, which wouldn’t surprise me. I don’t think I’ve ever heard anything good about TN Arms. I’m surprised they’re still in business.
Make sure the disconnector spring is installed. This is most likely an issue with the disconnector. As another member stated, it’s allowing the hammer to follow the bolt. If everything checks out with the fire control group, it could possibly be the spacing of the hammer/trigger retaining pin holes, which wouldn’t surprise me. I don’t think I’ve ever heard anything good about TN Arms. I’m surprised they’re still in business.
This first...
After that - if the disconnector is at fault - It is not at all hard to properly time one.
UTShooter71
08-27-20, 13:23
The disconnect or spring was bad (crushed). I missed this when I was assisting in putting it together. Talk about amateur hour. I did inspect the rest of the FCG and there is nothing out of order, damaged, or out of spec when compared to other parts. I have a replacement and will be trying it out again at my next trip to the range.
The disconnect or spring was bad (crushed). I missed this when I was assisting in putting it together. Talk about amateur hour. I did inspect the rest of the FCG and there is nothing out of order, damaged, or out of spec when compared to other parts. I have a replacement and will be trying it out again at my next trip to the range.Glad you found the culprit. Does it now reset correctly when dry firing, etc?
UTShooter71
08-27-20, 19:04
Glad you found the culprit. Does it now reset correctly when dry firing, etc?
I will post it as soon as it is back together. I'm hopeful.
The disconnect or spring was bad (crushed). I missed this when I was assisting in putting it together. Talk about amateur hour. I did inspect the rest of the FCG and there is nothing out of order, damaged, or out of spec when compared to other parts. I have a replacement and will be trying it out again at my next trip to the range.
I’d throw it in the garbage and put in a FCG of known quality.. ie Geissele ssa or budget g2s.
Your lower receiver hammer and trigger pin holes could also be off. It doesn't take much wear to take out a lower from pin wear or mislocated holes.
UTShooter71
09-08-20, 10:40
Tennessee Arms lower reassembled with all new parts kit. New brace on the way as well. The lower function checks okay: hammer locks back; safety engages; so on. After I have the brace installed and can function check it with an upper I will get it to the range and report further. Thanks for the assistance.
Sounds like the issue is resolved but just as a reminder to any one:
http://https://www.m4carbine.net/showthread.php?171260-Public-Service-Announcment-check-for-fire-on-release-triggers
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