Yeah, whatever.
It was a full metal jacket and designed to stay pristine on impact with the human body, per Geneva convention rules. Many bullets removed from soldiers in war are pristine. So, in your world someone fired the bullet out of Oswalds gun and into a water tank, collected it, then approached the gurney holding Kennedy and laid it next to his body. This plan to plant the bullet was all laid out before Kennedy was shot. If a pristine bullet is so unusual how come these genius conspirators didn't use a damaged bullet? Sorry, I find the pristine bullet much easier to believe. If you ever get a chance, catch the NOVA program on the Kennedy assassination. They actually showed that a pristine bullet was more likely than a damaged one.