Nine times out of ten the reason for brass that will not chamber is improper set up of the resizing die. Make sure you are bumping the shoulder back far enough when you FL size your brass. Tell us how you have your FL die set up, what kind of dies and press. Also make sure that the inside of the neck is clean and has a slight amount of lube. Pulling the expander button back through the neck can pull the shoulder forward.

My guess is you need to turn your FL die in more so as to bump the shoulder back! Or, if these are loaded rounds make sure that you have the seating die set up high enough to eliminate any chance of an unwanted crimp.