I lived in the USA for a couple of years and when I came back I brought two cap-and-ball revolvers with my household goods. I had done none of the paperwork in advance, I declared them at time of import and left them in trust at the border crossing. I filed the paperwork once I got moved into my new place, waited for the registration certs and an ATT to arrive, then drove back to the border crossing and picked them up.
This was all in 2002.