Hello, I put together my first AR last week.  Got everything prepped and lubed, and went to the range today.  Worked great for about 55 rounds, and basically started to FTE.  Federal LC XM193 was the ammo, which I understand should burn clean.

The first time, the bolt looked like it cycled, but didn't fully, because the round stayed hooked to the bolt and nothing tried to feed from the mag.  Second shot, it went back and stayed about 3/4 of the way back, and I finished the cycle with the handle.  The last time, it went only halfway back.  It was easy to finish the stroke with the charging handle, ejected nicely, and fed properly.  Figured I'd stop there.

They said, check the gas tube for fouling.  I said "After just 50 rounds?  Brand new?"  They said sure.  But, this doesn't add up -- wouldn't the bolt stay forward or come back forward on the spring alone if the gas pressure to push it back was insufficent?  Seems that the carrier sticking back is something else.

Any thoughts?  I'm new to this, don't really want to take off the gas block rail and such to remove the free float tube and check the gas tube if that sounds unlikely...

I'd appreciate your input.

-Dan

Check your gas rings.  You may have gotten a bad set.  Insert the bolt into the carrier without the cam pin, and hold it upside down.  If the bolt falls out, you need new rings.  Check also the carrier key.  Make sure the screws are tight and that it isn't fouled.  Your buffer spring may also be a factor but I doubt that.  

Since you had normal performance for about 50 rounds, a part must be defective.  The gas tube doesn't really foul as the high pressure and temperature don't make it such an accommodating place for crap to build up.  What brand is your weapon, the parts kit, etc.?  Oh, and also make sure to try different brands of ammunition.

It's a Fulton Armory upper (bought assembled) and a RRA lower and parts kit with a match trigger.

After all is said and done, it appears to be an issue where the constant cleaning I was doing during the barrel break-in was breaking down the lubricant.  When I finally tore it completely down, I found that the inside of the upper and the bolt assembly was a tad sticky, almost tacky.  I can't tell if there's another issue but I will lubricate it properly and take it out for another test run.  Past that I'll call fulton and ask their advice.

Thanks!

-Dan