Originally Posted by Robert Prey
Unlike exit wounds, entrance wounds do not "extrude."
From:
Understanding Injuries > Entrance and Exit Wounds
Entrance and Exit Wounds
Author: Jack Claridge - Updated: 20 July 2010
Entrance Wounds
The entrance wound is normally smaller and quite symmetrical in comparison to the exit wound, which can sometimes be ragged with skin, tissue, and muscle and bone damage. Entrance wounds are often ringed with the residue of gunpowder and cordite - the two substances contained within a bullet.
Exit Wounds
Exit wounds - as we have already mentioned - are usually larger than the entrance wound and this is because as the round moves through the body of the victim it slows down and explodes within the tissue and surrounding muscle. This slowing down of the projectile means that as it reaches the end of its trajectory it has to force harder to push through. This equates to the exit wound normally looking larger and considerably more destructive than its pre-cursor - the entrance wound.
http://www.exploreforensics.co.uk/entrance-and-exit-wounds.html