What's the general rule of thumb as far as deadly force use. If the aggressor is not armed as you are, when can you be justified in using a weapon against an unarmed but physically intimidating and aggressive perpetrator?
<- ex-cop, long time ccw'er.
Ok this varies by state, but here it is in a nutshell.
You have a self-defense claim for using force IF: you are "assaulted".
Lotta people think "assault" means they have to hit you first, or shoot first, but it isn't so. "Assault" is the crime of placing an innocent person in reasonable fear of imminent harm. Cocking a fist and stepping forward is an example of assault.
Like the "fire triangle", an assault claim requires three components.
The subject must have the Ability to harm you, he must have the Opportunity to harm you right now (imminent threat), and there must be an indication of Intent to harm you (also called Jeopardy).
Intent/Jeopardy: the subject must have made verbal threats, threatening gestures, or be acting in a clearly threatening manner.
Ability: the subject must have the ability to carry out the threat.
Opportunity: the subject must be able to carry out the threat right now, an Imminent threat... not a threat to kill you sometime later.
To pass for LETHAL self-defense, the threat must be of death or "grave bodily harm"... that latter term is subjective but typically means you are likely to suffer significant injury requiring medical treatment... more than just a black eye IOW.
All this must also pass the "Reasonable Man Test".... would a reasonable man in the same situation agree with your assessment of the threat?
BTW shooting is ALWAYS lethal force in the USA, do NOT claim you "shot to wound" (even if you did) it will ruin you in court. We "shoot to STOP".
Now in SOME states you have a "duty to retreat" before using lethal force, if possible to do so safely... this is very subjective and iffy and that's why a lot of states have removed the requirement.
And some states are more strict and prone to prosecute than others.
Final note: Relative ability is often taken into account. If a 100 pound woman shoots a 200 pound unarmed man acting like an imminent threat, she's probably ok in most states. If the physicality is roughly equal, then in some states you might be in need of a first-rate lawyer and some luck.