I don't agree with everything Lazs writes, but he's right about the difficulty of shooting at somebody running (unless he runs directly towards or from you) or shooting while running.
The difference between a gun and a knife is the amount of anger needed to commit a murder:
Gun: just a flash of anger may be enough to pull the trigger and deliver a lethal wound, because the action of pulling a trigger is somewhat distant of killing somebody.
Knife: the anger needs to be greater as the act of pushing several inches of steel inside someone's body is much more "personal" and goes against one's instincts.
Children show these barrier of instincts: their jaw is strong enough to tear chunks of meat from a steack but when they bite another kid they very rarely draw blood and only exceptionally tear the flesh.
The risk of committing something irreparable in a jolt of temper is hence higher with a gun.