Mighty Sling

This weapon’s damage is augmented by the wielder’s Strength bonus. For every two points of Strength above 10, add +1 to the damage dealt. (E.g., 12 STR = +1 Damage, 14 STR = +2 Damage, 16 STR = +3 Damage, etc.) If you’d prefer that expressed as a formula, use this:
(S-10)/2=B
S=total Strength; B=Strength Bonus.
Don’t forget to round down.

Strength does not affect this weapon’s To Hit bonus, only Damage is altered