Well, for us I don't list any finished gun as a whole gun, but rather as parts and the more details on the parts the less ??'s I get. For example:
Curly maple wooden stock, antique replica steel lock, brass castings, and 12L14 42" steel machined tubing.
Vague and truthful all at the same time.
First off ML guns are not classified as firearms so no need for us to call them that when trying to ship. They are classified as antique replicas, so refer to them as such and you can avoid triggering the gun freaks. If questioned, list out the parts above, still no reference to "a gun!"
It is completely legal to ship them through the USPS but you may need to educate your local staff by providing them with their own documents. UPS ships our stuff all the time, but being a privately owned company they can deny any gun, antique or not if they fee like it. We don't have any experience with Fed-Ex or other shippers.
All of our kits and a few lower priced finished guns are shipped in cardboard boxes stuffed with news paper. This has worked well for us for over 20 years now. If we are shipping any high end guns then we use an aluminum case from Kallispell with the option of the customer to buy it, or send it back at their expense.
This year however, UPS broke one of our kits and refused to pay the insurance claim of $250 to replace the stock. Their Claims/Insurance company is outsourced and thus not all agents are aware of UPS Field Rep. recommendations (our Rep. says news paper is fine - the claims agent said it's not). So after doing what we should have done years ago, we evaluated how much we spend a year in insurance from UPS verses the cost of the handful of broken stocks we get (typically one every 18 months.) When it was all down on paper UPS could break 10-15 stocks a year and we'd still come out ahead by not paying insurance on them. So we have completely dropped insurance on the rifle kits. Dad sent them a nice letter explaining how perhaps they should send their claims agents to a class on money management - pay $250 or loss $3000 seems clear to me, but not to the claims agent.
If shipping international just drop me an email and I can tell you how I'd ship your specific item.