I am glad that you made us aware of the problems going over the Dam. The last time I crossed I had a trunk full of ammunition in anticipation of a varmint hunt down in Texas. I was not stopped.
I have crossed the border into and out of Canada from Alaska, into Montana on the state side, and I am well aware of the limitation on the number of rounds of ammunition you are allowed, in Canada. That is right out of the "Canadian Firearms Commission" regulations. You must read carefully the regs each time you cross as there can be subtle changes to the laws governing transport of weapons and ammunition, and that includes total rounds of ammunition. They do not care what type it is, and they know the difference between .22 and .50cal when they enforce that part of the regs.
You can take rifles and shotguns across the border with the correct paperwork and a modest fee. Do Not even attempt to take a restricted or prohibited firearms across the border into Canada, and you can expect US Border Guards to be harder on you then the Canadians. Last time through I was checked by the Canadians on the way into the country, and by both border guards on the way out. The US Guards asked for my Canadian permits and verified that each weapon I said I had was correct, and the ammunition question put to me again.
My question would be why we have homeland security enforcing Canadian regulations within US Borders?
Another would be the lack of warnings to citizens about ammo restrictions. Will I need a passport to go from state to state and who will decided if I am allowed to proceed; the states or the feds?