So from what it sounds, is that when you fire the rifle the bolt carrier isn't moving at all, which means that the bolt carrier isn't getting any gas pressure to move it, or the bolt carrier is bound or has too much resistance to move rearward.
 
When teaching armorer courses, we recommend that you go through a process of checking things for narrowing down the possible causes.  You already mentioned that you have things lubricated.  You have already checked to make sure you have gas going through the gas port, and that the gas block is properly aligned over the gas port.
You state that the bolt carrier key screws (gas keys screws) are tight, but are they staked so they cannot come unscrewed?  Look at the sides of the bolt carrier key (gas key) and see if there are any signs of a gas like that would be coming out from underneath (it will look like a dark grey/black blast of carbon) at a rearward & downward 45-degree angle, which would be an indicator that you may have a broken screw.  Also if you have a pipe cleaner, then remove the bolt from the bolt carrier, and check to make sure that gas key isn't obstructed inside by pushing the pipe cleaner through the gas key and watch to see if it feeds it way into the inside of the bolt carrier.  Next check to make sure the gas tube is inserted into the gas block so that the gas port in the gas tube is facing downward towards the gas port in the barrel.  Check to make sure that the gas block is facing the right direction, meaning that some gas blocks will allow you to slide the gas tube all the way through the gas block and not have a stop built in, if you can slide the gas tube all the way through then you may have the gas block facing the wrong direction of which would block the gas pressure from going into the gas tube.  

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