You can make hit chance always count as unaimed or you can use....
calculation for average chance to hit: (correct me if I'm wrong)
20% unaimed, 10% eye, 10% head, 10% left arm, 10% right armo, %10 left leg, %10 right leg, %10 torso, 10% groin
let's say you have 95% when shooting unaimed but 10% when aimed eyes and 50% when aimed anywhere else
(95 * 0.2) + (10 * 0.1) + (50 * 0.1) + (50 * 0.1) + (50 * 0.1) + (50 * 0.1) + (50 * 0.1) + (50 * 0.1) + (50 * 0.1) = 55% average chance to hit
I think you can code this calculation to give you accurate display of hit chance with fast shot