I heard that they were seeing if other things could be as effective as cannonballs and these cannon firings were for setting the baseline speeds and force of a real cannonball. The local TV said it glanced off the berm , then up in the air, bounced in front of the house shown, through the front door, up the stairs, out the back wall, bounced on a 4 lane road, skimmed the tile roof of a house and landed in someone's SUV destroying the dashboard.
The Alameda Sheriff's PR spokesman is the liasion (sp?) with Mythbusters. He is at all their "experiments" okaying them.