Originally Posted by ISCS Yoda

There might be a time or a place for a warning shot (omitting animals; that's just such a different subject). Maybe. I am not sure what that time or place is. Where are you going to aim that shot? If you're standing in the middle of a yard with grass or dirt, okay, you could fire into the ground. Otherwise, where do you point it? Certainly not up. Certainly not at cement. Certainly not at your car. I do think that I could argue that if I'm at my front door and am confronted by someone in the street in front of my house I could successfully fire a round into the grass. But, as a normal, self defense thing, it's a total waste of time.

The guy has a knife. He's 20 or 25 feet away. Even 30 feet. You all know the drill, that a knife wielding bad guy can close that gap faster than you can get that second shot off. If you're going to play cop outside then you've decided to use deadly force. Use it, or stay inside, or go back inside. This is real world, not Hollyweird. Your gun is sufficient warning that you're prepared to use deadly force. If you're not thus prepared dial 911 and stay inside.

All the rest is commentary.