I've said it before and I'll say it again: hitting a prize with a broadside is far more than just ill advised. Its stupid. The ship you are trying to board is just as valuable - sometimes even more so - as the goods and/or people it carries so you better think long and hard before putting that slow match to the touch hole, mate.
But Pauline, you say, what to do when they start firing on us? Well there is that isn't there? And, though most pirates and privateers were too small to carry the kind of fire power that the movies - classic or not - like to show us, a couple of four to six pounders and a swivel could do a lot of damage if the need arose. Sometimes it did, and then the freebooters had to chose their ammunition wisely.
The options were not as limited as you might thing. As the Mythbusters proved a couple seasons ago in the Pirate Myths Revisited show, you can pretty much shoot anything out of a cannon (and hit a pig carcass with it). Hell, the Barbary pirates once shot a French governor out of a thirty-two pounder. Messy work, I'm guessing. Bottles, flatware, pins and needles, and the list goes on; anything you can cram into the barrel will, if properly primed, scatter menacingly toward the enemy. Of course, that doesn't mean it will do much damage and that is why there were different kinds of cannon shot for specific needs. You wouldn't hunt a squirrel with an elephant gun, after all (and if you would, I hope you live far away from me).
Pictured above are four of the five choices as far as ammo for your cannon. First off, of course, are cannon balls or round shot. This was used when serious damage to the prize was called for. Particularly, round shot was the weapon of choice against other cannons. A well placed shot could cripple or even blow up an opposing gun, with all the imaginable collateral damage. The problem was that ball would rust between uses and the rust had to be hammered off in order to insure that accurate firing could occur. That's fine in a chase situation where you have time to prepare for a potential battle, but not too handy in a pinch.
Next, the barbell looking item and its neighbor with the two balls and a chain are bar and chain shot, respectively. These lack the subtlety of ball shot and were used to cut up rigging, sails and any unfortunate sailors thereon. They spun and whistled horribly as they spewed from the cannon and merchant vessels feared the potential damage they could do to the point that they might just surrender if they saw bar or chain being loaded into a gun.
The white bags that look a little like something you might bring home from the feed store are grape shot. Round shot about the size of golf balls were tied together and fired at the prize. The bag burst open and the balls scattered, picking off men and rigging randomly.
Not shown is the dreaded canister, which was used exclusively for killing human beings. A cloth or metal container was filled with balls intended for flintlocks or muskets and fired at close range. The cannon was effectively transformed into a giant shotgun and the carnage could turn a small merchant into a floating abattoir with one or two shots.
Not pretty, of course, but a pirate ship is not a pleasure yacht is it? No it ain't.
And by the way, the picture shown today is from the drool-inducing sight Privateer Media. These guys will rent you cannons and shot and boats and so on for your next historical film. Go poke around. Trust me its fun (even if everything looks a little too clean).