Windsurgeon,
I have sold and shipped several rifles in the past few months - here is what I learned.
Two local UPS stores (within 10 miles of my house) would not accept them; they said only the UPS Hub would accept the rifles. The closest UPS Hub to me is 35 miles, so I did not want to use them. I used them several years ago, and they were a PITA.
So I now use the Post Office (USPS).
They do require a copy of the FFL held by the person/store/company to where the rifle will be shipped. The box is not to be marked or have any indications that it is a rifle.
A printed cell-phone color picture of the FFL was not accepted by my Post Office - they insisted on a faxed copy. (Hint: Do not argue with them.) Since I do not have a fax machine, I had the FFL holder fax the copy to my bank after first asking the bank if it was OK. This faxed copy was accepted by the Post Office even though the cell phone copy was better.
I have also received scanned copies of the FFL via email, and these have been accepted. Just in case, when I have received the FFL via email, whether as a pdf file or an image file, I have printed them in black & white as this looks more as a faxed copy. I do not know if this really makes any difference, but the last three shipments went along fine.
I have also received the full name and address of the person buying the rifle, and in each case have talked with them on the phone.
The shipping costs are not bad, and you can calculate them using the USPS website. HOWEVER, insurance is high, so be ready to pay more for insurance than for the actual shipment. I have shipped all the rifles Priority with signature required, which may be the only way they ship them.
Good luck.
Alex