Bottle-necked rifle cases are much easier to full-length resize if the cases are cleaned prior to sizing.

I clean my handgun cases to insure that no grit is present that might scratch the die. All brass is easy to clean by soaking in very hot water using liquid dishwashing detergent (the kind used in dishwashers), mixed with Lemishine, another dishwashing product. Then, allow the brass to thoroughly air dry. If in a hurry, you may bake them. You may also tumble the brass.