This is the right synopsis. I'm one of the gun nuts, but the firearms part of it is only relevant in this particular case to the extent to which it's introducing a highly lethal weapon into the altercation. There's some more legal niceties to the matter, but the bottom line from a standard legal and moral perspective is that you can't introduce lethal force to a confrontation where you had no reasonable belief that you would be grievously harmed and held innocent after the fact. I don't know whether that constitutes murder or manslaughter in local law, but it simply isn't an appropriate use of force.
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Godfuckingdamnit.
I'll be damned if that isn't the most Texas sequence of events imaginable.