Toby, I think if you look up history on this subject on this site you will find the proper explanation. It is easy to misunderstand and construe even by an attorney who does not read it closely. Center fire shotguns pre 1899 are still exempt. I don't recall the exact explanation but one of our members pointed out how it all makes sense. I would guess it was two pipes but not sure.

So many guns, so little time!