I have been playing games like MW2 recently and, as a programmer, I tend to ask myself how do they make the game so immersive. For example, how to they simulate bullet speed. 

1. When an NPC fires a bullet from his gun, does the bullet really travel from his gun to the given target or do they they completely ignore this part and just put a bullet hole on the target?
2. If the bullet is really travelling from the gun to the target, at what speed is it actually travelling?