Good point about upside down springs, Tikki.
From what I'm hearing, pulling the trigger fires a round then releasing the trigger fires another. If so it sure sounds like the disconnector to me - it grabs the hammer at first but the timing is off so it releases before the trigger sear catches the hammer.
You should be able to prove whether this is the case by removing the upper then cock the hammer and catch it with your thumb as you pull the trigger. Keep the trigger held back and recock the hammer so that the disconnector catches it then release the trigger. Be ready to catch the hammer again with your thumb if it doesn't get caught by the trigger sear. Do this repeatedly and see what happens. This is a test I perform repeatedly on new lowers I build to ensure they operate properly.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek
Last edited by Quentin; 08-25-2012 at 05:34 AM.