I think that a defensive firearm should, as a matter of policy be box-stock. What is interesting is that I have read Mas Ayoob say just about the same thing. You see, getting charged after a defensive shooting is not just a matter of murder versus no charges. If a gun has a lightened trigger pull, then there is always the danger of a manslaughter charge, based on the claim that the lightened trigger ("hair trigger" to a prosecuter and the uninformed) caused the gun to discharge accidently, resulting in the death of a "fine individual who was just getting his life turned around."
Mas actually recounts that he testified in a Miami, FL case, years ago, where a cop was being crucified over a shooting. At the time, Janet Reno was the DA for Dade County. The cop ultimately "won", after 3-4 years and two riots in Miami. You don't need to leave that opening.
In a related vein, never say, "I didn't intend to shoot him," because saying that is an admission of manslaughter/negligent homicide.
Also, how hard a time the DA gives you will depend on the jurisdiction. In Travis and Dallas counties in Texas, one is more likely to be charged, or have to spend $50,000 on lawyers than in most other counties. The joke is, shoot a burgler in Travis county and you will have to spend the next year in court. But, if you shoot a burgler in neighboring Williamson county, the police will critique your group and give you tips on accuracy for the next time. That is, of course, exaggerated, but it does illustrate that there is a difference, depending on the jurisdiction.
Gun laws are designed to extend and solidify the power of an elite over a peasantry.
Sauron lives, and his orc minions are on the march.