Your Form 6NIA, also allows you to purchase ammunition in the US, legally. The instructions on filling out the Form also indicate that you are not to export the ammunition. I just got back from 10 days shooting in Phoenix yesterday. When I headed south I had 4,500 rds of assorted ammo with me. As soon as I got down there I went looking for 12 gauge Winchester "AA" low velocity, low recoil for the wife. I had 600 rds of it with me but I found a flat for a good price and bought it. Winchester "AA" low velocity, low recoil is hard to find in Canada. During the 5 matches my wife and I shot we used the ammo that I purchased down there, then brought home the ammo that I originally took down with me. Totally legal.