A human(oid) body can only take so much damage from any one hit.  In particular, bullets, rayguns, and impaling weapons are likely to create a wound channel, then pop out the back.  The Blowthrough limit for a character is equal to his racial HP *or* the average for the weapon, whichever is greater (a battleship gun doesn't noticable blow through).  Damage from bullet or impaling weapons is capped at this much per hit.  The limbs have half the normal blowthrough limit, and extremeties have half of that.  The head has no blowthrough limit.

Note that most damage modifiers (like the x2 for Impaling damage, or the x1.5 for large-caliber bullets) apply to the Blowthrough limit as well.  So an arrow cannot do more than 20 points to the torso of a normal man, and a .45 slug cannot do more than 10 x 3/2 x 1/2 x 1/2 = 3.75 to the hand of a man.