Given the fact that we have a gazillion times more lawyers than we ever needed, and they are willing to do nearly ANYTHING to win a case, ethical or not, I consider the use of factory ammo a good idea. Overzealous prosecutors are a dime a dozen, trying to make a name for themselves, or for whatever reason. If they think they can make you look like some psycho whose intent was to waste a BG, they'll stoop that low. In a heartbeat. Maybe it goes with their own political agenda, or that of the local politicians. If the suitability of your ammo is called into question, the best defense is to be able to say you used that brand because the local PD does, or the FBI found it effective, or DOJ, or whoever. But if they can make you look like a nut case to a jury of people who don't know diddly about guns, ammo, justifiable shootings, or anything else relevant, they will.
It's my bacon on the line, so I choose to use Speer Gold Dots and Hydra-Shoks. I can defend its use easily. One less thing to worry about.
Papajohn