Ok, I've recently put together my first AR15 and everything looks great. However, took it to the range for the first time and ran into a problem.  The first shot went off great, ejected correctly,  and the second round seemed to chamber correctly.  But for some reason the trigger/hammer did not reset correctly.  I had to work the bolt manually to eject the unused cartridge and then let the next round load.  It would then fire correctly.  I basically could not shoot semi-auto.  I did notice that the second round always had a slight firing pin ding in the primer.

So what am I doing wrong here?  The bolt cycles and strips the next cartridge off the magazine but the hammer does not reset.  PLEASE HELP!  Thanks.
-NC_TarHeel

In the troubleshooting forum, theres a topic on "hammer failing to cock after firing".I had the same problem and researched the solution from this board.  Hope it helps...

Try your function test.

1. Remove magazine, un load and make sure weapon is cleared.

2. Pull changing handel all the way back and then let it forward.

3. Put safety on and pull trigger.  Hammer should not fall.

4. Put safety switch to fire.

5. Pull trigger.  Hammer should fall.

6. With trigger pulled to rear, pull charging handel to rear and let forward.

7. Release trigger.  You should hear a pronounced click but not as load as the hammer falling. This is the disconnecter catching the hammer.

8. Pull the trigger.  The hammer should drop.

If any part of this doesn't take place as outlined note which step and post back.

Halfcocked,
I followed your steps and the procedure failed at step 7.  I'm not hearing any click when I release the trigger.  What next?
-NC_TarHeel

Take the upper off, hold the trigger back and pull the hammer backand push it down until it catches on the disconnecter.  

When you take pressure off the hammer (keep pulling the trigger to the rear) does it stay back all the way?

If yes, let the trigger go.

Does the hammer move forward a little and then catch on the sear?

Halfcocked,
No, the hammer will not stay back when I take pressure off of it while holding the trigger back.

It sounds to me like your missing the disconnector spring, in the top of the trigger. I think you should just take the fire contols out, and reassemble again. [:\]

notack,
You nailed it!  But not before I figured it out by looking at some diagrams on ar15.com of the trigger assembly.  Thanks for your help.
I'm good to go.  
-NC_TarHeel