Since this is one of the grayest, "do as thou wilt" sections of the rules, I'm curious how everyone uses the aiming rules describe on page 201 of the Core Rulebook (no page number, just a pic of Han in Stormtrooper armor screaming at a complaining Chewbacca)..
Personally, I add a simple automatic effect, and then allow players to actually select specific critical injuries by
first activating a crit with their weapon
and
then
spending any extra Advantage, as follows;
Head Shots:
Add one extra Setback die (3 total, or 2 with double-aim); Automatic +1 damage; automatic Discouraging Wound critical injury or spend 1 extra Advantage for automatic Stunned or Head Ringer critical injury, 2 extra Advantages for automatic Overpowered critical injury, 3 extra Advantages for automatic Blinded or Knocked Senseless critical injury, 4 extra Advantage for automatic The End is Nigh critical injury, and 5 extra Advantages for automatic death.
Neck Shots:
Add two extra Setback dice (4 total, or 3 with double-aim); Automatic +1 damage; automatic Slightly Dazed or Winded critical injury, or spend 2 extra Advantages for automatic Knocked Senseless critical injury, 3 extra Advantages for automatic The End is Nigh critical injury, and 4 extra Advantages for automatic death.
Arm/Hand Shots: Automatically drop anything held in targeted limb; spend 1 extra Advantage for automatic Agonizing Wound critical injury, 2 extra Advantage for automatic Compromised critical injury, 3 extra Advantage for automatic Crippled critical injury, and 4 extra Advantage for automatic Maimed critical injury.
Torso Shots:
Automatic Stinger critical injury or spend 1 extra Advantage for automatic Agonizing Wound or Winded critical injury, 2 extra Advanages for automatic Compromised critical injury, 3 extra Advantages for automatic At the Brink critical injury, 4 extra Advantage for automatic Bleeding Out critical injury, and 5 extra Advantages for automatic The End is Nigh critical injury.
Leg/Foot Shots:
Automatically knocks target prone; spend 1 extra Advantage for automatic Hamstrung critical injury, 2 extra Advantages for automatic Compromised critical injury, 3 extra Advantages for automatic Crippled critical injury, and 4 extra Advtaneges for automatic Maimed critival injury.