Hey fellas, can someone here help me understand what's going on inside the bullet's head. We were talking about how a bullet at close range (high velocity) will (often) not expand. I understand the common sense end of it (bugs on the windshield), but what are the physics involved? Is there some type of "breaking point" at which the bullet will expand? Is there a certain velocity the bullet must be travelling when it meets a mass of certain density? Is there a formula to figure it out? The conversation that brought this on is below. Anyone have an intelligent explanation?