I had built 4 different AR's over the years.   Of all my AR's I've built, they've all functioned perfectly from day one.  

Last fall, I told my brother I was going to build another one, he excitedly asked me if I would walk him through it too!  And we'd each build one together.  Our step-dad caught wind of this, and wanted in as well, so now there are three!  We all went to gunshows, and shopped together, and this last christmas we put them all together.  My step-dad and I got a chance to go to the range with ours, but my brother was busy that day.  Our two builds functioned perfectly.

A week ago, my brother and I took his new build to the range and it would shoot two or three rounds, and then fail to go into battery completely.  Then one or two rounds would shoot fine, and then fail to go into battery again.  On one or two ocassions he'd get a light primer strike?

One problem that I instantly noticed was that we were shooting outside, and it was about 5 degrees out.   Also I found that he was shooting the gun completely dry (he had never put any oil on it since the build), and my oil was conveniently left on my shop bench and not with us that day!  Oops.

I've checked his gun over, it seems that the trigger assembly is properly assembled (trying to figure out the light primer strike), and the firing pin moves freely.

I'm thinking the failure to return to battery is a gas problem.  The key is properly staked to the bolt carrier, and the gas tube appears free of any kinks, or obstructions (although I can't say for sure on the obstrctions).  The bolt/bolt carrier moves freely onto the gas tube in the chamber, and doesn't bind up.

The only thing I've noticed is that the roll pin holding the gas tube to the gas block seems a bit "buggered" up, and tweeked.  It goes all the way through the gas tube, but looks a bit tweeked and doesn't exit the other side of the gas block.  Could this be a problem?

What else should I look for?  We've tried swapping mags, and only get problems in his AR, with any mags.  Could this all be a too cold and no lube problem?  Or could that roll pin cause this?

Any help is appreciated.  Thanks.

Hmmm...well a slightly short roll pin is probably not an issue but you can always put in a new one.  Remember to use roll pin punches for a better finish.

First thing is first....this gun should be stripped down, cleaned and OILED.  It sounds dry as hell.  I would also strip, clean and lightly oil the mags you are using.  I always over oil a new gun and fire the piss out of it for between 500 to a thousand rounds to really break it in.  After that, I clean it every time I shoot it.  Use a high quality oil like Slip 2000, Tetra, Snake Oil, etc.

If you continue to have issues then start looking at proper parts fitting, gas leakage, etc.

Quoted: Hmmm...well a slightly short roll pin is probably not an issue but you can always put in a new one.  Remember to use roll pin punches for a better finish. First thing is first....this gun should be stripped down, cleaned and OILED.  It sounds dry as hell.  I would also strip, clean and lightly oil the mags you are using.  I always over oil a new gun and fire the piss out of it for between 500 to a thousand rounds to really break it in.  After that, I clean it every time I shoot it.  Use a high quality oil like Slip 2000, Tetra, Snake Oil, etc. If you continue to have issues then start looking at proper parts fitting, gas leakage, etc.

+1 to that. It sounds like it's dry as hell. Spray down the bolt carrier and work the bolt back and forth, then shoot it. I'd be willing to bet that will take care of your problem.

Thanks guys.  I was/I'm really hoping that it's just a dry gun.  It was bone dry when he was shooting it, which is pretty much my fault because this is his first AR, and I assumed he'd oiled it up.

I don't see my little brother all that often (he's 28 and single, and lives 45 minutes away), so I was hoping to get as many ideas as possible to try the next time I see him.  I felt really bad for him, he was so excited to get it all built up, and then it didn't work perfectly.  Me being the big brother, I just want to fix it for him.

It maybe a tempature issue with the protectant they used or the oil you guys used maybe gelling up.

Us northern guys know about stuff like this dar hey. I would wait and shoot this weekend when it warms up and see if the same problem creaps up.

CLP Is all I use.

Good luck