I had to ship my franchi back to the manufacturer a few years back for a faulty firing pin issue that was covered under warranty. My franchi came in a padded gun box, so I broke the gun apart (O/U break action) and put the gun back in that box with extra padding so it absolutely wouldn’t move around at all.. Then I custom made a cardboard box around the gun case using a big old amazon cardboard box that a 50 lb bag of dog food came in. So I manually cut the box and folded it around the corners of the gun case. The end result was a super padded and protected outer layer around the already padded gun box. Might have been overkill but I wanted to be extra sure it’d be safe.
Also, USPS was the only courier I found that would ship a firearm without me being an FFL. I had to sign a form that said there was no ammo and it wasn’t a handgun or certain type of gun something like that. I believe franchi shipped it back to me via speedy.