I've spent a total of about 20 years prosecuting (and for a while defending) persons charged with crimes. Whenever one person fires a gun at another person, the law presumes knowledge that a likely consequence is serious physical harm or death. This is true whether it is a single-barrel .410 loaded with birdshot or a .223 semi-automatic rifle with a full clip of FMJs. Intent, on the other hand, depends more upon the surrounding circumstances. That is where the gun used can be suggestive. In my example, the .410 is not strongly indicative of a specific intent to kill, while the .223 is more indicative.

In many states, if there is evidence of an intent to kill and the claim is that self defense justified that intent, then the threat faced by the person must have been such that it would cause a reasonable person to respond with that degree of force. Most court decisions with which I am familiar recognize that you can't always pause to carefully consider the "correct" amount of force with which to counter an attack.

The "unknown intruder in the middle of the night" scenario is not one that poses a problem for a prosecutor. The breaks typically go to the homeowner, not the burglar. It is the far more frequent shooting "in self defense" following an argument or series of arguments between the parties that turns the black and white of the law into shifting shades of gray.