Oldest Style
If the bullet nose is rounded it is considered ball ammo. Ball is the oldest style of rifle ammunition, dating back to the early days of firearms.
Small Dimple
Hollow point (HP) bullets have an opening, or small dimple, at the top of the bullet. The metal around the dimple may be scored in a variety of patterns, and there may even be a small post of plastic or metal inset into the dimple.
Pass Through
Ball ammo does not expand when hitting an object. Because of its streamlined shape, it may pass completely through an object, retaining much of its energy and endangering whatever is in its path after it passes through the target.
Expansion
HP bullets are designed to expand upon hitting something. The scores allow the metal tip to fold back like flower petals, and act like a brake or parachute. This lessens the opportunity for a pass through, and dumps the energy completely into the target. The bullet's expansion also makes it more likely to hit a vital point within the target.