There Comes a Reckoning
Pages 133-134 of the Player’s Guide
After a successful attack, the shooter rolls location and takes into account the cover of the target. So if the character is leaning around a corner and has only his head and right arm exposed and the location roll is the left arm, the bullet hits the cover and the shooter rolls a d6: 1-3 the round is deflected, 4-6 it gets through the cover to hit the target but the damage is reduced by the “armor” value of the intervening cover.
Each level of armor value reduces the die type of damage rolled. If the die type is reduced to less than d4 it cannot do damage.
Wood less than 1" thick (most business and house walls) is Armor value 1
1-3" of solid wood, tin is Armor value 2
4-6" of solid wood, thin metal is Armor Value 3
A small tree, bricks, an iron pan is Armor Value 4
A large tree, armored train walls are Armor Value 5
Inch-thick steel plate is Armor Value 6
If you are actively participating in a firefight from behind cover, your head and shooting arm are exposed and you must take a multiple action penalty if you want to fire then duck back fully behind cover, or vice-versa