I see the term "casting" used a couple times here, but I believe this button is a "stamped" brass two piece type.
Rauville, I think you are right about this Type II. The Type I would be cast I think.
The one problem is that even if it turns out to be old...it has been cleaned up to look new.
Not cleaned up by me, that would be a big no no!! 
are you telling us Kevin ...that you are a Clarty..booger...
...you might have to google that.....
