projectile physics - How are bullets simulated in video games?

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?

   
   

Answer

Most FPS games use raycasting for the actual gameplay; bullets instantly travel and hit the target when fired.

But most games also employ the use of "fake" tracers. Every 3 shots, or some other interval, a tracer will be fired along with the bullet, the tracer will be really fast, but not instantaneous. This is done as a visual effect only, and does not affect the game-play directly, but helps give cues to the shooter, the shootee, and gives bystanders a directional reference to gunshots.

Most games that use these kinds of bullet physics are unrealistic, as there is no ricochets, no bullet fragments, and if there is any penetration its usually linear.

Some games, such as ARMA II, STALKER(entire series) use more realistic bullet physics with travel time, ricochets, and penetration with deflection angles. I believe these systems are using raycasting, but with a limit that is determined by the speed of the bullet. With these games the muzzle velocity can be realistic as in ARMA II, or looks about right as in STALKER.

I greatly prefer having realistic bullet physics, as guns fire projectiles, not lasers.