Time for the greatest hits,
Shotgun the rifle open and check the following.
Bolt will hand engage into and out of the barrel extension without binding (read bolt does not bind on the side of the lugs as it enter and exit.
Point the muzzle down 45*, pull the carrier all the way back against the charging handle and let go. The carrier should free drop down and lock the bolt all by it's self.
Look down at the back of the disco behind the hook; if you see a white line or dent, you need to take .040 off the tail of the hammer (carrier/hammer/disco wedge binding).
Pull the buffer and check the recoils spring at the very end of the last wind (receiver side), and take a look inside of the receiver extension. If you find a bur/high spot on the spring, or if the inside of the receiver extension has scrap marks, you need to correct the end of spring.
Spray CLP into the gas tube. The CLP should flow into the bore of the barrel.
Last item that comes to mind it to make sure that you have cleaned and lubed the weapon correctly using CLP (BreakfreeCLP) as the lube/cleaner. the bore will need to be cleaned with a copper solvent, but make sure that you have flushed out all the solvent with CLP after you have completed cleaning the barrel bore. Also, remember to apply a light Coat of CLP to ALL the bearing surfaces of the rifle/upper when you lube the rifle!!!!
Once you have done all this, you need to check the weapon for short stroking by loading a single round in the mag, charge and fire the weapon, and then confirm that the bolt has locked back on empty mag via the bolt hold open device. If the bolt does not lock back, pull the buffer, take all the weights out of the buffer (read make sure to reinstall the bumper end) and do the short stroke test again. In regards to the test ammo for the short stroke test, use XM-193 ammo (read buy a box if needed for this testing).