Then explain it to those who know little of ballistics.
He/she can't.
The heavy jacketed Carcano round that passed through something like 17 layers of clothing, Kennedy's neck and vertebrae, Connoly's body and wrist and into his leg while remaining basically intact is most certainly NOT the same type of round that his Kennedy's head and broke up, sending lead everywhere.
I myself, don't know what happened that day. I do know that the official story is incorrect (since there are two official stories, at least one of then has to be incorrect by definition). I also know, that anyone who makes absolute claims is suspicious or an idiot. Perhaps idiot is not the correct pejorative, but you get my point.