In my system I am addopting some of the rules from Night Bane for point blank and head shots, and some from what I have seen and done in the past.
For point blank rules, I say it is close then ten feet, more about three or four feet away, this means a person can parry the gun or weapon away from them, and it means they are not hit. You use your standard parry rules and bonuses. Damage from point blank is double damage from the weapon if the person is wairing armor, and it is hit, or damage to SDC and then half of that to hit points.
Example: David turns a corner and John is waiting there with a shot gun, John fires and hits David, point blank for 20 points of damage. David is not wairing armor, so he takes 20 to his SDC and 10 to his hitpoints.
Call shot rule for my system is that you need to roll a 15 or better to hit the spot, if you roll a 12 to 14 you hit the target, just not where you called. For head, and hands and stuff, there is still a -3 to the overall roll. Other areas like the leg are only a called shot. Also people of Good Alinment, and Unperinsapled people will NOT aim for the head in most events.
For head shots, you take full damage strait to hit pionts and double that to your SDC. This would also work for heart shots, or other vital organs. The GM should always have options for things like Leg and Arm shots.
Example: David is still kicking and takes aim at John's Head, hitting it for 12 points. So 12 points to his Hitpoints and 24 to his SDC.