The following is from the 2019 Spring issue of "The Artilleryman" Magazine Vol. 40, No. 2 by David Gotter
A canister round was a thin-walled metal cylinder packed with musket balls, or large lead or iron balls, and sawdust. Depending on bore diameter, typical Civil War canister shot was as small as .65 inch and as large as 2 inches. Some canister rounds have been found that were packed with nails, pieces of hinges, and other scrap metal. A round wooden block, or “sabot,” was attached to the bottom of the canister. The sabot helped to keep the round centered in the bore and also prevented the propellant gases from shooting out around the sides of the canister. Attached to the bottom of the sabot was the cloth bag that contained the powder that propelled the round. When the powder ignited, the force of the explosion would burst the can and the shot would spray out of the muzzle of the cannon with a murderous effect. “The enemy fell like grass before the mower.” “It seemed as if whole companies were wiped out of existence.” These quotes from Civil War soldiers are typical descriptions of the effect of canister. Canister was the artillerymans most lethal load and probably killed more Civil War soldiers than all other types of artillery rounds combined. Canister was only effective at short ranges, 400 yards or less, but like a blast from a giant sawed-off shotgun, the mass of slugs from the round would spread out and decimate everything downrange. When the enemy was within 150 yards, soldiers would load the guns with two or even three rounds of canister and fire them all at once.