Slightly more flare and what everyone else said.

I use Lee liquid alox and sometimes a buildup of wax will cause a similar problem.

I have an old sized 45 case that I cut some grooves into the open end of the case. As such it acts as a "shaver".

My last step in the reloading process is to turn this case over the newly loaded bullet. It will shave off any excess lead or lube. Have not had a chambering problem since I initiated this procedure.

As an aside, no matter what caliber, when I finish a day's loading I always take the seating / crimping die apart and clean it with a brass brush.