[ahakki]

IIRC IANAL: in a self defence situation you are required to use the least amount of force necessary or run away if possible (e.g. someone threatens to stab you in an alley. You may shoot them only if you can't escape. And you may only shoot them if there was no other option). The castle doctrine removes the «try to run away first» part, because it is not reasonable to expect someone to flee thier own home.

Stand-Your-Ground laws remove the «escape first» part outside of the home aswell.

You are always required to only respond with appropriate force. So you may not gun down someone who isn't a threat to your life.