Dennis here is a reply to an e-mail I sent to a fellow US shooter who has been going to Rosebud on a regular basis.
A U.S. citizen needs to declare firearms at U.S. Customs (airport, border) so they can bring the guns back in to the U.S. without paying duty (and no hassles for any other issues); proves ownership. This ony needs to be done once for each firearm, no cost, just keep the declaration for each gun. Of course, have to declare guns (up to 3) on the Canadian side - $25, good for 60 days. I have never had a problem, either country. Once the Canadian border folks start checking the guns, they move my extra wine out of the way (I wonder what the import duty is on an extra bottle of wine, but have never been charged!). Once I was asked by the Canadians about ammo - I explained that I had bullets and powder to load at the match, no loaded ammo. No problem. On the way back into the US, I have never been checked; I just say I have some rifles that I have declared, a liter of Canadian Club and I'm gone. Once, the US patrol guy paused, then asked why I had rifles in July (not hunting season). I said I had been at the Canadian Nat'l. Benchrest Championships, he asked how I had done, I said I won (2007), he said congratulations and I was off!
That be the reply from a fellow US shooter. Sounds straight forward and fairly simple.
Calvin