Keep in mind also that if you cannot afford an expert witness, you can spend a few minutes establishing the credentials of an expert and then introduce passages from their books and training manuals, clarifying the point that one round is rarely enough to stop a determined attacker, and that you should fire till the attacker is down. You can also introduce passages from police academy training manuals to the same effect. A smart prosecutor would not wish to open the door to such evidence, however, which is why a smart prosecutor would not imply that you were blood thirsty because you fired more than one round. This implication opens the door to a mountain of experts to the contrary, making the prosecutor look ignorant. By the way, prosecutors are not allowed to communicate to the jury any "information" about the effectiveness of handguns or laser sights. That would be considered testimony (or, if merely implied in a question, "assuming facts not in evidence"), and attorneys on both sides are barred from doing that.