One: the transfer of energy causes a change in momentum. Basic physics - anyone who has used a rifle observes this.
Two: for the "escaping brain tissue" to cause motion, the head would have to be acting like a rocket or a balloon. The tissue moves in the direction of the bullet because the bullet has imparted energy to move it in that direction, and the whole head moves as well in that direction. When material escapes from an exit wound, it is NOT acting like a rocket. It is a collection of material moving along the 'momentum path'of the bullet.
You are describing a physical impossibility.
you're not good at it.
and Luis Alverez agrees with me.
(MVC)
The Pristine Bullit Corp. makes a series of pristine bullits,...
........ called, "Whip-lash Mags"., for special 'far-out' pigeons and turkeys.
(Money back guarantee if no 'Whip-lash' occurs.)
:-)
/sarcasm