Soory, may be I didn't use the good word. I thinked that canister is some box with lot of pieces of metal inside, like lead or steel. Your put the canister inside the canon like a boulet. But when you fired you throw lot of metal's pieces in lot of direction front of you and probably kill or injury lot of people in the same time.
In french we call that "mitraille" and the gun who could fire lot of bulette in the short time is a "mitraillette" (machine gun in english).
Stéphane