@RanchRoper , I can't help you with the legal issues. I hope some of our Canadian members can comment on that.
I've used .480 balls in a .50 caliber rifle. Conventional wisdom maintains a very tight ball/patch combination gives best accuracy, but personally, I'm willing to sacrifice a little accuracy for easier loading, especially if a quick reload is needed. This was not a particularly accurate load, but it was adequate for my purposes and was definitely preferable to struggling with the ramrod. As
@Walkingeagle suggested, a thicker patch of .020" or even .018" might be needed. I think I was using .018" with the .480 balls, and saw no evidence of blow-by or gas cutting. A bonus is that a thicker patch will hold more lube. Always a good thing.
I believe the old-timers probably shot smaller balls, relative to bore size, than is recommended now. For example, reading I have done recently indicates the service load for the .54 caliber US military rifles intended for patched round balls used a .525" ball, or .015" under bore size. Captain Dillin told us it was common to find more than one ball size in old hunting pouches... One size for accuracy, and the other for a quick reload. If .480" balls are the closest you can get, I think you should have no qualms about getting them, and spend some quality time on the range experimenting with patch material.
I have done some casting. I like the old Lyman Ideal lead ladle, but with the pouring spout drilled out to a little larger diameter for a faster flow in pouring. I use a Coleman camp stove (the old-fashioned kind that requires pumping the fuel tank to pressurize it), a cast-iron pot from Lee Precision, and beeswax for flux. With a piece of broomstick to gently knock the sprue cutter and a folded towel to catch the hot balls, you're good to go. The hardest part, right now, may be finding a mould!
Good luck with it, and by all means, let us know how things work out.
Notchy Bob