Nothing is random, it's physics. Bullet is fired from one spot at the certain speed speed, altitude, and distance, it hits the prop (or what ever) at a certain spot, bases on that specific prop, and speed that it's moving at it might simply depart the airplane (and hit something else on it's way) or just take damage.
there is your randomness right there...projectile hitting a prop blade does not have an exact result...the result is a random event.
ever notice that hits produce either exact damage or none at all? hit the top of a cylinder head with a .30 cal round, depending on velocity and angle of deflection, it may nor may not cause damage to the engine...if it deflects, it could exit the cowling, or bounce around inside the compartment, maybe hit a fuel line or wire...whatever it hits while it's bouncing around, it may or may not cause damage...that is the randomness.
just from my observation, an engine hit produces 1 of 2 results...oil leak, or engine dies...no engine fire, no rough running from a blown cylinder, no electrical malfunctions.
maybe random was the wrong word to use...perhaps variables would have been proper...there aren't a lot of variables to the damage system. that sound better?
perhaps a wish for more extensive damage variables is in order...broken gun sight, damaged gauges, engine fire, electrical malfunction, prop damage, etc...etc..etc..