A bullet with a "hollow tip" is called a hollow point. Other points for handgun bullets are Soft Point, Round Nose, Wad Cutter, Semi-Wad Cutter, and Spire Point. Some bullets are Full Metal Jacket, Lead - either Copper washed or natural, Jacketed or half-jacketed, each with a point designed for a specific purpose. You may have found a .22 rim fire cartridge.
The major reason for most bullet designs are based on the need for rapid or slow expansion at the target. Hollow points are expected to expand well but, at handgun (low) velocities, they often fail to expand at all so it's largely physycological for the shooter.
Cartridges may be loaded with any of these bullets. None are illegal. Yet.
Last edited by 1hole; 10-18-2007 at 06:16 PM.