The ballistic model is also detailed, taking into account drag coefficient properties, muzzle velocity, and mass of each individual type of ammunition. The game engine considers the physical details of all rounds in flight and at point of impact, calculating the angle of impact and energy of the round, and the thickness and slope of the target vehicle's armor. Rounds which manage to penetrate may go on to cause damage to components or crew members in the path of penetration. High energy rounds that do not fully penetrate may still cause spall (high velocity metal fragments) within the vehicle, if close enough to penetration. Rounds that penetrate a vehicle will usually leave a visible hole on the outside, while rounds that don't penetrate may leave a scuff mark where the round bounced off. Small arms fire will also often leave bullet holes or scuff marks on buildings or vehicles.