I have a bit of an obsession with d6s, they are by far my favorite dice. As a result, when making house rules I usually only use six siders. I've messed around with a number of d6 based systems for combat before, and decided to share some that work.
D6 combat systems (to hit and armor)
X in 6 to hit, armor as damage reduction
Everybody has a 3 in 6 chance to hit, except fighters, who have a 4 in 6 chance. Basically, roll 1d6, if it is 3 or lower, you roll damage. Light armor subtracts 1 point of damage, medium armor subtracts 2 points of damage, heavy armor subtracts 3 points of damage. Shields can be broken to block all damage entirely.
3+ to hit unarmored
Roll 1d6 to hit. If attacking an unarmored target, you need 3+ to hit. For a lightly armored target, you need 4+, medium armor needs 5+, heavy armor needs 6+. Shields can be broken to block an attack.
3+ to hit, armor as temporary hit points
Roll 1d6 to hit, on a 3+ you hit. Armor acts as temporary HP to block damage, like in the first edition of the Black Hack. The armor points “heal” to maximum at the beginning of each encounter. If the system normally uses descending AC, armor points are determined by subtracting the AC from 10. If the system normally uses ascending AC, armor points are determined by subtracting 10 from the AC.
Automatically hit, armor as damage reduction
Just roll damage, ignore an attack roll. Light armor blocks 1 point of damage, medium armor blocks 2 points of damage, heavy armor blocks 3 points of damage. Shields can be broken to block all damage.
D6 combat systems (damage)
D6 plus modifiers
Damage value is d3 for unarmed attacks, d6-1 (minimum 1) for light weapons, d6 for 1 handed weapons, d6+1 for 2 handed weapons, d6+2 for heavy 2 handed weapons.
2d6 drop the lowest for heavy weapons
Damage value is d3 for unarmed attacks, d6 for a 1 handed weapon, 2d6 drop the lowest for a 2 handed weapon.