Problems with my first pistol build?

Jbram40 said:

So I just built my first AR pistol. Stag arms lower, Anderson LPK, shore tactical upper 10.5" carbine length gas .223 wylde, pistol buffer kit.

I shot it once and the first 40 round mag all fired no issue, but for some reason the next mag would shoot once. It cycled the next round but the trigger didn't reset. I had to pull the charging handle and eject a fresh round and then it would fire one more and do the same thing.

I got the carbine length gas because I heard it creates a more reliable weapon, but is the fact that I have carbine gas system and a heavy pistol buffer the reason the bcg isn't going back far enough to reset the trigger?

Thanks

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HordesOfKailas said:

So you're saying it ejected the spent case and loaded the next round but didn't reset the trigger? Were both mags loaded with the same ammo? Are the mags the same brand?

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Pitbull410 said:

I'm not an expert at all but I believe I've read the cause of this on other sites could be an improperly installed trigger/hammer spring. Specifically an upside down spring. Something to check atleast, sorry if I'm way off.

Sorry I don't know specific terminology

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Jbram40 said:

Already checked it all out but I will look again. Had a buddy who has assembled multiple ar's walk me through. The fact that it shot the first 40 round mag no problem is really what has me confused

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Pitbull410 said:

I'm not an expert at all but I believe I've read the cause of this on other sites could be an improperly installed trigger/hammer spring. Specifically an upside down spring. Something to check atleast, sorry if I'm way off.

Sorry I don't know specific terminology

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HordesOfKailas said:

This was my thought as well. Check the trigger assembly.

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Jbram40 said:

Already checked it all out but I will look again. Had a buddy who has assembled multiple ar's walk me through. The fact that it shot the first 40 round mag no problem is really what has me confused

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Melnic said:

I"m not an expert eather but i've built a few ARs and debugged a number of issues (with the help of fellow MDSers)
did you load up the first mag and try again, thus isolating it to the 2nd mag only?

I have only giessell triggers so yours may be different but my trigger resets with the bolt about half way back.
This I expect to happen before the round gets ejected.

You can look at how this works this with an unloaded AR.

Verify gun is unloaded
Pull charging handle back.
Safety off
Pull trigger and hold trigger back (you should have heard a click), don't let go.
Slowly pull charging handle backwards and listen for the click
Note how far bolt goes back when you do this. With my giesselle, the bolt goes about half way.
Let bolt go all the way forward.
Now let go of trigger and you should feel/hear a 2nd click.

If you don't hear that 2nd click, the disconnector is not letting go when it should.
If you don't hear that 2nd click, but pushing the trigger forward makes it click, again, that confirms the disconnector is not working properly.

The disconnector test can easily be done with just the lower and holding onto the hammer. Look for videos on this test on youtube.
I simply suggested doing it above so you can see how far back the bolt needs to go to have the disconnector hold onto the hammer.
My point being if your ejecting a round, the buffer/spring/gas should not be the issue for the trigger not resetting when letting go of the trigger.

I had a disconnector timing issue on a lower kit build once and the 2nd click yeilded the hammer going all the way down (would cause a 2nd round to be fired when releasing trigger). In my case, the disconnector piece was out of spec. I ground it down it to make it work to verify it was the issue, asked the MFG to send me a new one which they did. 2 weeks later put in a giesselle cause I like them so much.

Somewhat helpful video on standard trigger and disconnector
https://www.youtube.com/watch?v=s2vL_Yu6rYU

This is not your problem but doing this test will show you how far back the bolt needs to go for a trigger to reset.
In my case, the trigger is reset even when the bolt can short stroke.

You know you have a gas/spring/buffer/undergass situation when you fire one round in the mag and the bolt does not hold open.
What I have done in the past on a new AR build per a suggestion from others is to shoot 10 rounds one at a time, each time the bolt should be held open.

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