Playing the "killer bullet" card would be something played out by an ignorant attorney. An astute attorney could demolish most of the arguments with facts. A quick shut down would be-" I picked Hydra shok (gold dot, corbon et al) because the police here use it.
" I loaded the gun with the ammunition I had on hand" would probably work just as well. A good way to sell ammunition, if perchance a gunwriter happened to be a distributor of a particular brand of ammunition, might be to discourage the use of handloads while promoting the favored brand.
Of course, nothing like this has ever happened, God doesn't make little green apples and it don't rain in Indianapolis in the summer time.