in Texas, the law is pretty clear that you may not use lethal force (gun or whatever) against another unless that person:
A. Has the ability to inflict serious bodily injury to you or some other person.
B. Is in position to do so.
C. Has indicated intent to do so in some way.
An example would be an adversary with, say, a tire iron, who A) is big enough to swing that tire iron and injure you; B) is close enough to reach you with it within a second or two; and C) is, say, focused on you and is running toward you swinging it. At that point, you can draw your gun and fire in self defense.
Note that you don’t have to wait for them to hurt you or your loved ones. But the above conditions generally must be met before you can legally open fire. There are specific exceptions to this in Texas; for instance, if someone breaks into your home in the middle of the night, and you feel threatened, the three conditions are assumed to be met.
Disclaimer: I am not a lawyer. Do not make any assumption about the validity of these statements – read the law yourself, or get legal advice from somebody qualified. You never know, I may be mistaken.
This post may have some bearing on your thinking on the previous post.