This has been done to death here, and on other boards.
[1] I'm a lawyer (retired after over 30 years of practice), and I'm also a shooter and NRA certified instructor.
[2] I don’t use handloads for self defense purpose.
[3] It's not about the gun or ammunition per se. It's about how certain factors, like tinkering with your gun, using handloaded ammunition, putting "Punisher" grips on your gun, walking around wearing a "Kill Them All and Let God Sort it Out" T-shirt at the mall, or other "gun nut" stuff can be used to attack your character and credibility. This is important because if you're in trial at all, somebody in authority thinks that your claim of self defense is vulnerable, and your testimony might be crucial to establishing that your use of lethal force was justified. If the jury can be convinced by the prosecutor that you're a junior Rambo wannabe, they just might not be inclined to believe your story.
[4] Yes, I know “this doesn’t matter if it’s a good shoot.” And I agree, it doesn’t matter if it’s a good shoot; but who decides if it's a good shoot? Nobody has to take your word for it. Whether or not it's a good shoot can be uncertain. Physical evidence may be lacking. There may be witnesses who tell conflicting stories. In any case, if everyone agrees it's a good shoot, you go home. But if you're on trial, someone in authority doesn't think it's a good shoot. In that case, whether or not it was a good shoot will be decided by a jury; and they may just need to believe your testimony in order to find that it was a good shoot. So anything that can impair your credibility increases your risk of a bad result.
[5] At a trial, at the end of the presentation of evidence, each side gets to argue what the trier of fact should infer from the evidence. So a prosecutor might argue that a trier of fact should infer certain things about your character and disposition for violence from the evidence that you handloaded yourself the ammunition you used. Indeed, I'd expect a prosecutor to conjure up for the jury the image of you up late at night in your garage quietly assembling special super killer bullets.
[6] So Suzy Soccermom now asks herself, as she sits on your jury deciding whether to believe your story about what happened when you shot that nice gang member, why store bought ammunition wasn’t lethal enough to satisfy your perverted blood lust. Remember, Suzi Soccermom and her friends are going to be deciding if the shoot was good.
[7] Yes, we know that there doesn't appear to be a case documenting this, but this would be a trial court matter, and trial court activities are not well publicized or generally published in the official legal reporters. Only decisions of courts of appeals on matters of law are regularly published. In any case, I suspect that the great majority of private citizens who own guns for self defense, including those with CCWs, are not necessarily enthusiasts. They most likely own and carry factory stock guns loaded with ordinary, commercial ammunition. So in fact, it's pretty unlikely that there have been too many cases, if any at all, in which a modified pistol or handloaded ammunition were used.
[8] Of course, if one is unlucky enough to be on trial, whether or not he used handloads would be only a perhaps small factor. But personally, I'd rather avoid any of these sorts of "wild cards" altogether. Even though I may have an explanation, I know from experience that the less I have to explain, the better off I am.
[9] And most of the explanations we might have for using handloads are just too “inside baseball” for people who aren’t shooting hobbyists or gun aficionados to pay attention to or care about. And if you’re on trial, it’s most likely that most of your jury won’t know much about guns, will have no, or little, experience with guns, and may perhaps have doubts about whether private citizens ought to even have guns. So if you make an argument like, “I used handloads because I wanted to be certain the bullet would perform optimally in my gun and for my shooting style”, you’ll see their eyes glaze over like the Easter ham.
[10] I don’t see that I gain anything using handloads for self defense compared with quality, commercial ammunition. If I have to use my gun to defend myself, it is a certainty that my conduct will be subject to intense investigation by the police and the district attorney. It is very likely that my conduct will come before the grand jury. It is a distinct possibility that I will be required to answer criminal charges and also defend my conduct against a civil claim for damages. My freedom and property will be at risk. I will have to spend at least tens of thousands of dollars, and possibly a hundred thousand dollars or more, to defend myself. So it strikes me as prudent to do what I reasonably can do ahead of time to lay as good a foundation as possible for a good result for me.
[11] This is just what I do and why, based on my training and experience in the legal profession. Each of you may, of course, make his or her own choice.