You mentioned you don't have a barrel on there yet, are the bolt lugs dragging across the feed ramps?
Is you buffer tube and buffer/ spring detent installed properly?
Remove the upper from the lower, remove the charging handle, insert BCG and move back and forth, see if it is hanging up anywhere in the movement. Remove BCG and insert the CH move that back and forth, see if it is binding anywhere in the movement.
If everything seems GTG and moves without any issues, check you lower. Start with the Bolt catch, is it seated properly, does it move without binding. Do a function check on FCG, check hammer spring make sure it is installed correctly.
ETA definately that nub on the CH, grind it off, sand smooth, GTG