Steve;
About 12 years ago, I learned the difficult way that some USPS clerks go berserk if you tell them you have a gun in a package, and even some postmasters don't believe that it is legal and within USPS rules for a private citizen to ship a long gun to a FFL dealer. In the past I have printed the USPS Domestic Mail manual section on shipping firearms and carried it with me to the post office to show the clerks who are ignorant of USPS regulations.
I do not do anything now but take the package with the long gun into the post office and hand it over for their processing--this is all you have to do according to my interpretation of USPS regulations. The USPS clerks are obligated to ask you their standard questions about if the contents are hazardous and so forth, but you are not obligated to inform them that the contents is a long gun, according to my interpretations.
I just sent packages to a FFL dealer and acted just as I described above, with the exception that I insured the package.
I suggest that you google the USPS domestic mail manual and read up on what you and the USPS requirements are in accordance to your question. I am assuming that you understand that you must be shipping to a FFL and that you need to have a current copy of his/her FFL to protect your interest.
I recall years back when I showed the relevant USPS domestic mail paragraphs to the the USPS clerk (after she refused to take the package) that she was shocked and told me that she had always been told by the postmaster that a private person could not ship a firearm of any sort. Keep quite and do not muddy the water, also if you are shipping to a FFL that it's company name references guns, arms, firearms and so forth, do not use that portion of the title. In my experience it is best to address it to the individual at the address--all of this is to minimize theft inside the USPS. Also ship the package on the first day of the week where there will be little likelyhood of the package spending the week-end in a postal facility--waiting to be stolen.
Been there done that
Last edited by bushveld; 06/07/18 01:33 PM.