Sometimes things will dry fire function fine but under live fire the violence of the gun cycling cause the failure.
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Pins all tight?
Slightly sticky hammer/disconnector interface? I've had to smooth a couple of those out.
As gotm4 said - It sounds like the disconnector isn't engaging and the hammer is following the bolt forward.
When you cock the action with the charging handle the hammer rotates rearward and engages and the main (lower) sear.
When the bolt moves rearward after firing it rotates the hammer rearward and the disconnector engages the hook on the rear of the hammer.
Letting off the trigger to allow it to reset lets the hammer fall slightly and once again engage the main sear.
Pull the lower off and you can work the mechanism manually and see if the disconnector is sticky etc. Moving the hammer rearward should engage the main sear which it obviously does. Moving the hammer rearward with the trigger pulled and the hammer should engage the disconnector. Allowing the trigger to reset and the hammer should engage the main sear.
Does the trigger reset after firing the first live round? If not, it could be a bad trigger spring.
To take a different tack, what kind of gas block are you using and how sure are you that it's properly aligned?
If I'm getting this right (the trigger resets when cycling by hand, but not with live rounds) it's possible that the gun is getting enough gas to feed/eject rounds, but not enough to drive the bolt carrier far enough back to cock the hammer.
This does not need to be a free for all.
If you have not dealt with and corrected this problem, your input is less than valuable. Before you post, read the entire thread.
OP-
We need a detailed description, and preferably pics of what is going on, both dry and live, to make an accurate diagnosis. gotm4 (who does not need my backing) is one of the most competant AR smiths I know and should be considered the primary trouble-shooter on the forum.
it seems like it has progressively improved with manual/dry manipulation. my thoughts are that things were a bit tight and catching. will be going to my range today. i will post a very detailed report of what the firearm does. i tore everything down, hit some contact point with a dremmel/polishing pad/rouge, lightly lubed it, and dry cycled it. everything seems a bit smoother. the trigger sticks for a SPLIT second before reset. i will put the weapon through its paces and report back exactly what happens.
Gents,
It is EXTREMELY helpful if you can articulate or show pics if possible when trying to isolate these kinds of problems. Using the correct terminology and nomeclature will aslo go along way as well.
FWIW- if you the hammer had been in the forward position after you fired the round (i.e. it followed the firing pin) but didn't fire. I would have guessed we were possibly dealing with a bolt bounce issue.