I would like to swap shotgun barrels with a fellow who lives in Canada....they are both Beretta 391 barrels. Is it possible just to send them thru the mail or is it more involved than than? If so, how can we do the trade?

its pefectly legal from the canadian perspective, but if you are in the US and have a ffl you would be braking YOUR laws. If the deal is beween private partys, it might or might not be legal, I know people buy barrels on ebay in the US and have them shipped here.

If you want to know for sure you might want to contact the ATF.

I believe that you need a export permit from u.s. customs
there has been problems with guys bringing gun parts from
the u.s. into canada. u.s. customs have stopped people coming into canada and seizing firearm related items its so bad cabelas won't ship into canada anymore