Just use UPS or Fed Ex and you will have no problems. I mail pistols occasionally, just take them to the local UPS customer center, which is like a mile from my house
and tell the guy it's a gun and I'm sending it to the manufacturer or an FFL, whatever.
Maybe because I live in a relatively small town (our UPS office is in a trailer... LOL) and they are used to rednecks with guns. Probably would be a different story if I was trying to mail in San Francisco.
Heck I just realized the last gun I shipped (last Friday) I didn't even mention whether it was loaded or unloaded and the clerk didn't ask. LOL