One Final Comment...
Since I started all this, let me just say that I wrapped up the rifle, padded it well, taped it up with a whole bunch of different kinds - filament tape around it, plastic tape everywhere - and took it to the P.O. The affable and really nice clerk asked me if there was anything hazardous, dangerous or fattening (could be wrong on that one); I said no (and it was true, nothing remotely connected to firearms) and he cherrily posted it off to the addressee. End of journey. Guy who bought it was happy, I was happy, and the P.O. was blissfully unaware and officially o.k. with that. Just my experience, and hopefully it will be yours.
Finis.
P.S. Regarding paper tape: back in the day, we sent classified material - Confidential only, inCONUS - via registered mail, and we had to use paper tape, with water-based glue. Reason: you can't fiddle with it without destroying it or making it obvious that you've fiddled. I was in the sneaky branch of intel and it was pretty much impossible to get into it surreptiously (note: not impossible, just pretty much).