Complex sentence: Bullet wounds vary in how much they incapacitate an assailant and the greater the injury inflicted, the greater the chance of killing one's assailant or wounding him so badly he is no longer able to fight.
Split into simpler sentences: Bullet wounds vary in how much they incapacitate an assailant. The greater the injury inflicted, the greater the chance of killing one's assailant or wounding him so badly he is no longer able to fight.