A recent experiment by the Mythbusters recently went horribly wrong, with a cannonball leaving the Alameda bomb range and striking a house and Minivan. Hopefully this will not end the popular TV show.
More information here: http://laslow.net/2011/12/07/mythbusters-and-damage-control/.
The news story is here: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/12/07/BA1D1M99V5.DTL. This goes to show that even a small cannonball can have a huge amount of momentum and carry it a long way, this is why the ancient sailing ships were so effective at damaging each other, the power of the cannon balls was able to punch through the wooden hulls very effectively. This is a picture of a cannon ball about the same size of the one that the Mythbusters used. The ball is quite small, but if it was going at 500 feet per second, then it would go straight through you. There is also chain-shot which uses two projectiles joined by a chain that can cut right through anything it strikes. Pretty horrible if you fired it at a group of charging soldiers.