I shipped a barreled action to ER Shaw back in August via USPS, and the post office was very confused about the entire matter. The lady at the counter kept telling me that she needed "a form". I asked what form she needed, to which she replied "I don't know."
After reminding her several times that it was going to a gunsmith, that I owned it, and it would be returned to me, so there was no transfer occurring, she eventually asked me to stand aside so she could go in back and research it. About 5-10 minutes later she came back to the counter and said she could send it. All told, it took about 45 minutes from the time I stepped into the post office. It was an exercise in patience to be sure.