What brand of receiver and trigger group?  Any chance you could post a pic, looking from the top down at the trigger group system, as this may help us see what may be going on?  Could be a badly machined receiver, safety selector, trigger and/or hammer.  

For process of elimination, I would suggest removing the hammer, trigger and disconnector, and give the receiver and trigger group a good cleaning and inspection.  By removing the trigger group you will be able to see if there is any type of obstruction underneath like a blown primer, broken hammer or trigger pin, etc.c.  With it removed, inspect the hammer and trigger for any possibly broken or damaged areas where the hammer & trigger have physical contact with each other (Sear engagement).  Make sure the trigger reset spring is installed correctly.  Then try dry fitting just the trigger into the receiver, it should not be rubbing or sticking against the sides of the receiver walls.  Try dry fitting the top back end of the trigger into the middle of the safety selector channel where the trigger goes up into when firing, it should move freely and not stick or rub.  Try inserting the hammer & trigger pins into the trigger and hammer, and see if they rotate freely or get stuck.



CY6
Greg Sullivan "Sully"
SLR15 Rifles
DefensiveEdge.com
(763) 712-0123