[@ihinka]

While entirely possible, the individual ball bearings are very, very small, not to mention fragile. They're about as big as a squirrel's eye, so at best you have a very light object that will have questionable trajectory and not nearly enough mass do much notable penetration through the force of a sling alone. Now tossing a whole sack of ball bearings, that's potentially more effective simply due the collective concussive force of the bag, though don't expect a shotgun explosion or anything like that.