The short answer is: if a threat has the "means, opportunity, and intent"1 to cause severe bodily harm or death, then I'm justified in using deadly force to defend myself and others. This also presumes that I've exhausted my options for escape and employing force of a lesser degree. Fortunately, in Colorado, we do not have a duty to retreat but I'd be remiss not to advise my fellow readers to
just walk away if they are afforded that option. The best gunfight is the one you're not in!
Yup, that's the short answer. (Can you tell that I teach this stuff?)
Long answer? Hire an attorney to give you a rundown of your state's "use of deadly force" laws. If you CCW, you have that attorney on speed-dial already, right?
I agree. "Walk away if you can" is the very best advice on this topic.
TCM
1 Believe it or not, these terms have legal definitions. Your attorney can elaborate...