Need help solving AR build problem

[GunOwner]

I have a problem with a recent build. The bolt binds and sticks as I try to pull the charging handle back. The lower is Superior Arms I have done builds with them before and never had an issue. So far I have done the following:

Tried the upper from this problem build on another lower - no problem - worked fine.
Tried an upper known to function properly on this problem build lower - same binding problem.

So I think I have eliminated the upper and/or BCG as the issue.

I replaced the collapsible stock with one known to work and verified proper spring length/coils and buffer.

So I think that is eliminated.

Now I am stumped - could the lower be bad? How would I verify?

Could one of the other components in the lower (hammer, bolt catch or ?) be causing the problem. I have done a number of builds they have all worked fine so far but that doesn't mean I didn't screw this up.

[bryant]

you said you try know upper that working and lower ar working just fine, try to swap bcg, try to elimanated if bcg is the problem.

[GunOwner]

you said you try know upper that working and lower ar working just fine, try to swap bcg, try to elimanated if bcg is the problem.

Thanks - did that - BCG not the problem.

[DFence]

Sounds like the buffer is binding up in the tube.

Possible that the threads for the buffer tube are slightly threaded wrong causing the tube to be out of spec.

Check and see if the tube is square with the lower receiver when installed. Then check and see if the buffer will cycle back and forth by hand. Use a cleaning rod or something to push it into the tube while on the lower.

[starsnuffer]

Buffer tube and bolt catch are two things I can think of here. It may be the tube or the buffer retaining detent. Do you have another buffer tube from another lower you can check?

-W

[GunOwner]

Buffer tube and bolt catch are two things I can think of here. It may be the tube or the buffer retaining detent. Do you have another buffer tube from another lower you can check?

-W

I swapped in a known to work collapsible stock, spring and buffer - verified straight - cycled the buffer/spring back to verify no binding before attaching upper - attached upper - - still same problem.

I don't think it is the buffer detent because I can pull the bolt back about 1.5 inches before it binds a lot so the bottom of the bolt clears the detent before it really binds badly and at that point the BCG does not touch the detent.

How can I test eliminate the bolt catch?

[Army]

Make sure your disconnect spring is not kinked and is fully seated correctly. Also make sure the pistol grip bolt is not too far inside the receiver.

[Gutz]

I'm going to bet on the buffer tube spring binding or the indent catching the BCG.

The forward assist is not catching anything, is it? Thought I'd throw that out there.

[ohlone]

i have similar problem once, it was the buffer retainer was a bit too high and got in the way of bcg. the stock tube needed to be turned a bit more to push down the retainer a bit more.
that was my case......

[sdfire]

Try using a different bolt catch. Sometimes they are wider ,or not cut at the right angle, and you will get this problem. Try removing the bolt catch , leave it out , and see if the bolt does not bind. Then you will know if that is the problem.

[sean714]

sounds like a buffer tube problem to me, check that retainer like ohlone said.

[5.56Geo]

Almost the same problem with by brothers AR. He replaced the buffer tube and the problem went away.

[GunOwner]

Thanks for all these suggestions. I have tried all of them without success.

Here is another tidbit. If I just hold the upper to the lower unpinned the bolt will cycle fine (it looks like the upper separates from the lower in the back ever so slightly)

When I pin the lower and upper together no go.

Also there is a bit of wear on the bottom of the buffer tube.

I think the lower might be slightly out of spec. Thoughts?

[tpat663]

I had this problem and it was the hammer, it was out if spec and caused the same issue. Try a different hammer. Good luck.

[gemini1]

^ I was also gonna suggest the hammer. take it out and see if it still binds