Well I nominate 500 Raj (or if you decide later on a different calibre(s) then it would be 577 / 600 Raj etc
If it's a Howdah then the old tiger leaping onto the back of an elephant springs straight to mind & only a Raj was wealthy enough to afford such a weapon to defend the townspeople to do so!
Will be interesting to see where this project goes, all the best on your endeavours.