New at this

[Phil C]

Personally I will not ship a shotgun in an assembled state. For a SXS I remove the barrels and forend from the receiver/ butt stock assembly. Wrapping each them separately in a cardboard box designed for firearm shipping.
I make sure to remove the tension of the top lever so it comes back to neutral. I ship by Priority mail, signature required, and ask that the FFL inspects the package before signing for it.
It will be impossible to make a claim if the package is signed for and later they report the box was damaged along with the firearm when the box was opened.
Ship insured unless you have a personal gun policy that covers guns if damaged or lost in shipping.
Quality Packing material and a strong container is money well spent.
Never underestimate the ability of any shipping company out there to be able to damage an item you ship and be done in ways you can not imagine.
Luckily for me I have only had 1 shotgun damaged that I personally packed and shipped.