Since cannons have been mentioned, I thought I would add the following from the Battle of Antietam/Sharpsburg:
The batteries were soon firing double charges of canister from the red hot barrels. Gunners avoided the time consuming task of swabbing the barrels after each discharge by “thumbing the vents”, a dangerous process by which a gunner kept his thumb over the gun vent to prevent oxygen from entering the chamber and setting off the charge prematurely while the loaders tamped in powder and shot. When the gunner removed his thumb the cannon immediately fired. Firing these heavy double canister loads, made the gun recoil four or five feet and the gunner who was firing with his thumb had to ride the gun back. A commander of a Federal regiment facing this onslaught commented later that the artillery fire coming out of the orchard was the most effective he had ever experienced and that no one could survive its’ fire.
(Source: "Warrior In Gray - General Robert Rodes of Lee's Army" by James K. Swisher)