A bullet with a hollow inside and serated tip that, upon impact with a viable target, gets twisted inside out, forming a very large mushroom shape, thus increasing the caliber of the bullet dramatically. This results in either a HUGE
exit wound, or
it stays in the body, causing
certain death. Very expensive. 25 bucks for a box of 20 rounds. Really good for self defense though. Really good if you intend to put someone down with only one shot.