Nice cannon! My buddy's father used to work for a local Hercules plant and get us cannon grade black powder. His cannon was cast iron with a steel sleeve, poured at a local foundry, had a 2-1/2" bore.
Pyrodex is kinda pricey. I'm thinking of trying some Goex Reenactor in my black powder revolver, only $12.99lb. Hazmat would be a killer unless I order a bunch. https://www.grafs.com/retail/catalog/product/productId/23159