Basically, think of it as a big spike in pressure in the blood and other fluids, it can cause incapacitation instantly.
Since tissue is mostly liquids it can affect all organs at once, but mainly the brain and CNS.
It's hard to predict, but 243 should do it. I've seen eyes pop out from it, and it wigs me out LOL.
I don't know all of the specifics, but I think bullet constuction has a lot to do with it .