AR build issues

[AK0perator47]

I have just came back from the range. My AR build is able to fire the first round and it picks up the second round but, the trigger is dead. I am curious to know what is going on.

The lower is a Spikes Tactical with a Maxim Defense CQB stock. The upper is my Bushmaster 16" barrel.

I am not sure if it's the buffer or the trigger. Here is a video that may help. Anything else that would help you help me just ask.

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[DirectDrive]

First, verify that your trigger is installed correctly...

 

[AK0perator47]

Yes the is installed correctly.

 

[Heyjoe]

I'd bet the trigger is failing to reset. Next time it happens try to push the trigger forward to help it reset. I do not know what causes this but I've seen it on more than one rifle. Always seems to go away with a little break in and oil.

 

[AK0perator47]

I'd bet the trigger is failing to reset. Next time it happens try to push the trigger forward to help it reset. I do not know what causes this but I've seen it on more than one rifle. Always seems to go away with a little break in and oil.

Good to know and I will check it out. Never had it happen before but will definitely see.

 

[Heyjoe]

Forgot to mention that you could dry fire it, holding the trigger down, cycle the bolt and release the trigger to diagnose this issue. So you don't necessarily need to be at the range. It may or may not behave the same way dry firing but it's worth a shot.


Edit: is the trigger milspec? Maybe it's a good time to polish engagement surfaces with emory cloth.

 

[AK0perator47]

Yes mil spec and already polished it

 

[DirectDrive]

Forgot to mention that you could dry fire it, holding the trigger down, cycle the bolt and release the trigger to diagnose this issue. So you don't necessarily need to be at the range. It may or may not behave the same way dry firing but it's worth a shot.

This ^^^
If you can pull the BCG all the way and the trigger resets, but during live fire the trigger does not reset, you have narrowed it down a bit.
See what happens in the dry fire mode.

(also make sure that the disconnector is free and not bound up)

 

[AMProducts]

As @Heyjoe pointed out, you can absolutely do this "Dry fire". Standard test after building a lower (before you put the upper on) is to cock the hammer (with your hand), while your hand is still on top, pull the trigger and then push the hammer all the way back down until the disconnector engages it, repeat several times. When you put on the upper, without ammunition, pull the trigger and keep it held down, cycle the bolt, slowly release the trigger until the disconnector disengages, pull the trigger and cycle the bolt again.

If it's failing this test, there may be something wrong with the LPK, it could need polishing or something could be out of spec. The hook on the disconnector may be too long, the slot where the disconnector sits may be too deep, or the hole placement on either the trigger or the disconnector may be off. Either way, this is an essential set of checks to perform on any AR. It is also possible the disconnector isn't engaging, and you're lucky and not getting slam fires.

Given that we only saw one shot sample there (I'm guessing there were more), a full function test (NO AMMO!!!) is recommended. If possible, if you have another friend with an AR, or another ar, swap upper and lower groups and perform the dry test again. This may help.

There's also a very very slight possibility, that the gun isn't gassed properly, however since it seems to be picking up rounds from the mag I don't think that's the issue.

 

[AK0perator47]

I don't think the disconnector is unlatching allowing it to engage the sear.

If that's the case then polish it more or what?

 

[DirectDrive]

I don't think the disconnector is unlatching allowing it to engage the sear.

If that's the case then polish it more or what?

It has to fit in its pocket without binding.
So if it's too wide and binding you'll have to file it or replace it.

 

[bolus]

Does the second round have a dent in the primer? (hammer falling before the BCG is locked)

 

[AK0perator47]

Does the second round have a dent in the primer? (hammer falling before the BCG is locked)

it would appear so

 

[bolus]

View attachment 482774 it would appear so

one possibility is the hammer is not locking back on the sear and just chasing the BCG forward and resting on the firing pin.

Happened on my first 80% plastic receiver build (that I did a terrible job on) and the hammer pin hole was in the slightly wrong place.

Do you have another trigger group to put in there?

 

[AK0perator47]

one possibility is the hammer is not locking back on the sear and just chasing the BCG forward and resting on the firing pin.

Happened on my first 80% plastic receiver build (that I did a terrible job on) and the hammer pin hole was in the slightly wrong place.

Do you have another trigger group to put in there?

No I unfortunately don't have another... I plan on getting a drop in trigger but wanted something to work until I could afford it.

 

[titsonritz]

As @Heyjoe pointed out, you can absolutely do this "Dry fire". Standard test after building a lower (before you put the upper on) is to cock the hammer (with your hand), while your hand is still on top, pull the trigger and then push the hammer all the way back down until the disconnector engages it, repeat several times. When you put on the upper, without ammunition, pull the trigger and keep it held down, cycle the bolt, slowly release the trigger until the disconnector disengages, pull the trigger and cycle the bolt again.

If it's failing this test, there may be something wrong with the LPK, it could need polishing or something could be out of spec. The hook on the disconnector may be too long, the slot where the disconnector sits may be too deep, or the hole placement on either the trigger or the disconnector may be off. Either way, this is an essential set of checks to perform on any AR. It is also possible the disconnector isn't engaging, and you're lucky and not getting slam fires.

Given that we only saw one shot sample there (I'm guessing there were more), a full function test (NO AMMO!!!) is recommended. If possible, if you have another friend with an AR, or another ar, swap upper and lower groups and perform the dry test again. This may help.

There's also a very very slight possibility, that the gun isn't gassed properly, however since it seems to be picking up rounds from the mag I don't think that's the issue.

Do this standard function test.

What is your FCG? I would remove it and make certain your hammer spring and disconnecter spring are not installed backwards, if they are you correct you most likely have either and out of spec FCG or lower receiver.

 

[bolus]

No I unfortunately don't have another... I plan on getting a drop in trigger but wanted something to work until I could afford it.

I have an extra plain boring CMMG trigger (got a bunch of lower kits for spare parts when they were $20 each). If you dont get it figured out, let me know and I can mail you one of my spare triggers for free.

 

[AMProducts]

I installed a trigger spring backwards the other day (I caught it after I put the trigger in the gun and was like WTF). I've built hundreds of ARs in my time. Worth checking....

 

[AK0perator47]

I installed a trigger spring backwards the other day (I caught it after I put the trigger in the gun and was like WTF). I've built hundreds of ARs in my time. Worth checking....

I will take it apart.. having built a bunch it is frustrating when you try and figure out wth you did wrong! Lol

 

[AMProducts]

I will take it apart.. having built a bunch it is frustrating when you try and figure out wth you did wrong! Lol

I've got a 18" SPR build I've been working on, I needed it to do some longer range accuracy testing, it rarely gets through a 10rd mag without some kind of short-stroke, FTF, or FTE problem. Since I need it for accuracy testing, it hasn't been a super big issue (I can run it as a Straight-pull-bolt) but it's frustrating as hell.