Sorry, your gun is an interesting design and would make a good discussion topic but it does not appear to replicate a pre 1899 design and as such does not meet the criteria for posting on the GBO Blackpowder Mortar and Cannon forum. If you can provide a letter from ATF acknowledging that this gun is as a replica of Antique cannon then you can post on the Cannon board.
Here is a link to the rules for the board
Read and Heed! Board Rules found in the stickies at the top of our forum.
In the mean time I have moved you post to the exotic weapons board.