1) Roll for double shot
2) Roll for normal shot (eg. using the skill Pistol&Revolver)
3) If the roll for DoubleShot was successfull, the player will use two bullets no matter what, and it hit approximately the same place as with both bullets. Hence, if the rolls for Normal Shot is unsuccsessfull, both bullets are wasted. If the roll for Normal Shot is successfull and hits the opponents left leg, the successing bullet wil also hit the left leg because there is no time to change targets.
4) Roll for damage for both bullets.
The best way to use this skill I believe is aiming for the opponents chest which is fairly easy to hit. A must-have skill when going up against the really strong opponents.