Aiming:

A 1 second aiming time with an 80% accurate weapon:

Shooting Skill 5:
Body size 0.5: Final aim time is 2.07 .
Body size 1: Final aim time is 1.65.
Body size 2: Final aim time is 0.81.

Shooting Skill 10:
Body size 0.5: Final aim time is 1.76 .
Body size 1: Final aim time is 1.40.
Body size 2: Final aim time is 0.68.

Shooting Skill 20:
Body size 0.5: Final aim time is 1.12 .
Body size 1: Final aim time is 0.90.
Body size 2: Final aim time is 0.44.

Shooting:

For accuracies less than 1, weapon accuracy increased towards 1.
70% weapon accuracy, final accuracy becomes 0.925.
80% weapon accuracy, final accuracy becomes 0.95.
90% weapon accuracy, final accuracy becomes 0.975.

Shooter Skill: See the table in the settings for the accuracy at each skill level!

Accuracy * Shooter Skill * Cover * Weather * Gas (and other misc modifiers) = To-Hit Chance

Cover:

When targeting someone in 50% cover.
Sight 50%: Actual cover 84%.
Sight 100%: Actual cover 50%.
Sight 150%: Actual cover 38%.