I believe that it is/was Mossad Ayoob that did a write up about an actual case where the shooter, acting in self defense, got railroaded because he was shooting a 10mm Auto using handloads. Or something similar (it was awhile ago I read this and the details are fuzzy). The "problem" for this guy was that the prosecution/plaintiff argued that his choice of caliber (10mm Auto), and the ammo he used (in this case it was Winchester Black Talons I believe) intentionally made his gun somehow more lethal than other handguns, thereby implying that he intended not simply to stop the attack, but rather to kill the attacker. Therefore, by selecting said caliber and ammo he intended to use excessive force and was criminally and civilly liable for the death of the perpetrator.
Anyway, I do recall that he, with the supporting recommendation from both civil and criminal defense lawyers, concluded that the best bet of a civilian to protect themselves from legal problems after a self defense shooting was to carry the same caliber, and if possible, use the same ammo as what is used by your local law enforcement agency. The thought is that if it's not excessive force for a cop to shoot an aggressor with that caliber and type of ammo, then it's not excessive force for a civilian to do it, too.
Mike