This cannon is made from 4140 hex stock steel.This is a salute cannon great for parties and holidays.It is extremely loud.It is 11 1/2 inch long,1 3/4 inch wide,9 1/2 inch chamber with a 3/4 inch bore.
His description leaves one wondering what exactly the barrel dimensions are. Is the 9 a typo? Or does he mean the tube is 9.5" long with a .75" bore? Is the 1.75" width of the barrel or the whole thing, carriage included? A .75" bore should have a 2.25" outside diameter chamber since one can never be sure that a device like this will never be fired with a projectile, notwithstanding eBay's silly rules.
So for us to give useful help, we need to know the barrel diameter and the bore diameter.
I consider FFFg powder to be too fine; FFg, or better Fg, would be my recommendation. Look in the stickies at the top of the forum for loading procedures. The charge should be firmly rammed but not more than once and not pounded tight. I wouldn't use more than one square of dry TP as a wad. If you use the recommended aluminum foil powder bag, you really don't need a wad.
Also, since you don't say where you live, check the local laws before getting too carried away with this. The socialist republic of Massachusetts has strict rules about firing a cannon if you live in that benighted state.