You are watching an old movie, The Day of The Jackal² starring Edward Fox as an assassin.    He commissions a rifle hand-made to his own specifications, cartridges for it also specially made.
       The gunsmith queries - “Will you go for a head shot or a chest shot ?”.
       “Probably head” . . . .
       “In that case you'd better have explosive bullets".
       “Glycerin or mercury ?".
       “Oh, mercury . . . I think.    It’s much cleaner !”.

       The assassin goes into woods to centre the rifle's scope.   He hangs a water-melon, on which are painted eyes, a nose and mouth, from the branch of a tree, and strides seventy paces away.   Strapping the rifle, loaded with a full-metal-jacket round, to a tree trunk for support, he aims and fires.   The slug puts a small hole in the water-melon by its right cheek ; the gun is firing low and left.    Using a screwdriver he adjusts the rifle’s scope and fires again, the second shot hitting higher, to the side of its right eye.    After a final adjustment to a different screw his third shot hits between the eyes.    The target now has three holes drilled through it :  low on its right, higher on its right, dead centre.
       He takes a different cartridge, a frangible round previously wrapped in tissue paper, loads, aims and fires.    The water-melon explodes.

       You have just witnessed the different effects of, first, a full-metal-jacket³ bullet and, second, a frangible⁴, or explosive, bullet.    Full-metal-jacket bullets are designed to pass clean through a body, causing minimal damage, temporarily disabling and allowing the target a reasonable chance of recovery.   Frangible bullets are soft-nosed or hollow-point ; they disintegrate on impact, exploding into many minor fragments, their forward velocity causing massive damage.