Re: 308 Neck Sizing Issues
I agree FL size to normally avoid problems.
However, in this case something sounds familiar, especially if a unloaded case will chamber but a loaded one will not. That is not normally a shoulder bump issue when that happens. Either the empty cases will chamber or they will not without difficulty.
Did you trim/rechamfer the necks after FL sizing?
Take a loaded round and run your fingernail from the shoulder to the bullet and see if you feel as slight ridge at the very edge of the brass at the top of the neck.
IF you do, you have a problem with your neck chamfering tool rolling the outside neck rim over very slightly instead of cutting it cleanly. Mine was a 40 year old tool, that once replaced and necks rechamfered, solved the problem.
I have seen it twice and it happened to me last summer. I had to take nail file and file off the ridge on the loaded rounds at a match.
The resized cases chambered perfectly BUT when you put a bullet in them, that ridge stood out enough to hinder chambering. The empty case easily squeezed down until you put a bullet in it.
Just something else to look at and easily find and fix.