I agree it may very well be a lubricant problem. I have a brand new unfired Colt Police Positive revolver that was made in the 20s. You can't cock it or even swing the cylinder out. I've chosen to leave it that way as it doesn't have a mark on it. The chambers still show 100% blueing.
Your gunsmith may be right about it needing a few hundred rounds to loosen it up but I personally would do a detailed cleaning before firing this gun.
Jim

The 2nd Amendment IS an unalienable right.