Venting atmosphere

Hey, above all, do not forget that the venting athmosphere of a penetrated spaceship will change it's course. Minimally for a small hole, dramaticaly if an compartment of the spaceship explodes completely.

Also space is not completely empty, there is minimal friction due to dust in space. If you shoot from earth to the moon with a normal handgun the bullet will most probably never reach the moon. It'll be slowed down and stopped by (A) the gravitation of earth and (B) by the random dust particles found in between.

Just my 2 cents.