CW,
I don't think the guns themselves would be off topic, they are pre 1899. It's the projectile that might be controlled, isn't it?
I agree, the projo's would be DD's (no pun intended).
It was the picture of the wheeled cannons that caught my eye. Something for which one could build a 'replica' thereof (using blackpowder though) to meet the BATF requirements. Not pretty, but an easy form to duplicate with an interesting history.
AND, I though some folks here might be able to answer this guy's question about the wheeled version.