This image depicts both the canister and the musket balls which are contained within the canister. The balls are packed with sawdust or gunpowder which burns up or explodes after the canister is fired from a cannon.
This is a Confederate 12 Pounder Canister Shot. It is similar to the one used to quell the rioters at the Cooper Street Armory during the Boston Draft Riot. But, at Cooper Street a 6-pound canister shot was used, half the size of this one. …