I heard a statistic the other day that there are something on the order of 300+ million firearms in the United States. I have no idea whether this count includes military and police weapons.

Passing a ban on firearms is a long shot. I think a much more realistic situation is a ban on ammunition & reloading supplies or else a sky-high tax (think "fee") on the same.

The guns won't be very useful if ammunition is hard to come by.

I don't know much about the United Kingdom or Australia, so hopefully someone can chime in here. Is outright ownership of a firearm illegal in and of itself? Or can folks own firearms but keep them in their homes for sporting purposes (target shooting, hunting, etc.)?