'pristine bullet' is not possible because no one has ever duplicated it or anything like it.
First of all, that's just factually wrong. See the Discovery Channel program
Inside The Target Car for a very close recreation of Oswald's second shot.
Second, many laymen just like you are led astray by their intuitions about probability. Seeming paradoxes, fallacies and misconceptions abound.
Here's an illustration. The chances of any specific person winning the lottery are infinitesmal. However, the chance that
someone will win the lottery is typically 100% (depending on how it is designed). So if you're running the lottery, you can't just tell the guy with the winning ticket "Sorry, but your chances were many millions to one. You must have cheated, so we're not paying!"
The assassination didn't
have to happen exactly the way it did. It just so happened that JFK was killed instantly and JBC was seriously wounded but survived. JFK
could have been killed without anyone else being hurt. Both JFK and JBC
could have been killed. Or Oswald might have missed entirely, just as he did with General Walker.
There were perhaps a dozen outcomes, each of which could have been realized in a million different ways: at slightly different times, with slightly different wound locations and a slightly different shape of the spent bullet, and so on. It necessarily follows that each of those million ways had a very small probability of happening -- yet it
did happen! So by demanding an exact recreation of the actual shot, you're simply missing the point.
Even Oswald himself could not have repeated any of his shots with
exactly the same results. Indeed, each of his shots had a very different result. That's how the real world works.
It's perfectly reasonable to ask if each bullet followed all the laws of physics. (Yes, they did). Beyond that, the only reasonable question is this: under the circumstances, did Oswald have a good chance of fatally hitting JFK at least once by firing three shots? Again, the answer is
Yes, as has been demonstrated countless times over the years by many marksmen using identical Carcano rifles and target speeds and distances.
And no, they
don't have to exactly duplicate the shape of CE399, because that's just one of the many ways it could have turned out. But the aforementioned Discovery Channel program came remarkably close. I recommend that program highly.