AR Problem - Help me! :)

[Danno]

OK, I just finished my AR last week - have not had a chance to shoot it yet, but in my fondling, I noticed a big problem. I will say this first - I purchased a complete lower, and complete upper - only "assembly was putting the two together.

So the problem: I pull the charging handle back, let it go, and the bolt doesn't go all the way forward. It stops about 1/2" from where it should be. After investigation, I found that the Buffer Retainer Pin was not staying down, and was getting caught on the bolt. I had to pull both take down pins to get the thing apart - it wasn't going anywhere...

Does anyone know why this is happening? I've double checked every part on that lower, and everything looks right, but I can't seem to figure out why this one pin is hanging up?

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Any help would be greatly appreciated!

 

[Thoth8]

who made the upper and who made the lower?
What kind of fit do they have ?

 

[KimberPB]

I'm going to look at mine when I get home but is there a burr on the bolt carrier that the pin maybe catching?

 

[KimberPB]

Actually are you sure it's hanging on the buffer tub pin?

Try this take:
Take the upper receiver and insert the bolt carrier group. Slowly push the bolt carrier forward. You should not feel it snag and it should take very little pressure for the bolt to engage the chamber. I can actually hold my upper at a 45 deg angle and the bolt will slide closed by itself.

You may have a burr in the upper receiver or more likely the gas tube is slightly out of alignment. Either could cause your issue.

 

[Red Hat]

That's my first guess, the gas key is not lining up with the gas tube. Look and see if the key or the tube has a smiley on it. If it's not lining up take a big screwdriver and bend the gas tube enough to line them up. The gas key should slide over the gas tube easily.

 

[Danno]

Thanks everyone for the input! Come to find out, the idiot that put my lower together (purchased already assembled) didn't screw in the buffer tube in far enough to hold down the buffer retainer pin, so it was popping out. Tightened up two turns, and all's good in Danno's AR world now

 

[AR Hammer]

DPMS let a BUNCH of buffer retainer pins out on the market that were too tall a few years back,
And I STILL run into them once in a while!

Glad to hear it was your buffer tube.
Makes for a quick fix when it's just adjustments!