I ship and receive antique guns USPS all the time and have never had a problem. I don't tell the employees what I'm shipping when I drop it off as it's really none of their business. However,I enclose a note in the packaging informing anyone that opens it that the enclosed firearm is an antique and exempt from any postal or federal firearms regulations.
Now if the idiots in charge would just permit me to do so with C&R firearms as well I would use them exclusively.
Jim
I use the USPS Registered Mail exclusively for C&R long guns.