One major problem faced by the Insurgents specifically was the lack of shrapnel rounds. Their suppliers and supporters in the United States did not think to send them these rounds, which would have been very useful when trying to dislodge the Spaniards from their trenches. Only canister and common shell were available to the Insurgents. Shell is an explosive projection which explodes on impact, set off by a percussion fuse. Shell is used against personnel, or fortifications.
Shrapnel is an anti-personnel round used at long ranges.
The shell bursts after a given amount of time, triggered by a timed fuze. Ideally, shrapnel would burst over the enemy troops, scattering deadly metal fragments. Canister is strictly an anti-personnel round. Canister is used at shorter ranges. All three types of projectiles are loaded into the gun as a cartridge, where the projectile and powder charge are already placed together, and set off by a firing pin in the gun.