That is a tough one, but first I would remove the scopes.
Plan on using UPS.
You are going to have to find some long boxes of some sort to customize and reuse.
At work they use these cardboard corners from uline for strapping stuff.
They happen to come in long boxes that are about 6x8 inches, made with really heavy cardboard.
I took one and shortened it, and then cut the box down the side where it is glued together.
Packed the gun into it, and taped it back together. I put some thick white foam in the ends of the box.
The 10 pound R1 I shipped , made it perfectly from Atlanta to Washington state.
Rick