Wrapping the factory box with brown shipping paper is a good plan.
Actually, that's not that great of a plan. The USPS recommends that you don't use wrapping paper, string, string tape, masking tape, or duct tape when mailing boxes. They get caught in the automation machines, and can very rapidly get crunched. Everything (including large parcels) are automated now. In San Diego alone, we process over 30 million pieces of mail per night.
I'd recomend turning the box inside out if it says "Winchester" or some such identification as a firearm. Personally I use 3M clear wrapping tape. It is stronger than the box.
I've shipped rifles many times, and don't hesitate to use the USPS. Just shipped a rifle this week.
Jeff
