Hail the return of Chainmail PDF, but I really don’t like weapon versus armor class tables for modifying hit probability in RPGs or wargames. Players don’t like doing math before they attack and often conveniently forget to apply penalties that effect combat resolution.
Therefore, after a successful hit, I allow rerolling of ‘1’s’ on the Damage Dice if an attack strikes a vulnerable opponent. Vulnerability is determining by comparing weapon versus armor type:
On the damage dice roll, ones will be rerolled if the attack is fire or cutting/ slashing in nature and the defender or target is wearing Soft armor.
On the damage dice roll, ones will be rerolled if the attack is acid, cold or piercing in nature and the defender or target is wearing Flexible armor.
On the damage dice roll, ones will be rerolled if attack is electricity, sonic or bludgeoning in nature and the defender or target is wearing Rigid armor.
When any die is rerolled, you must accept the result of the second roll. A die can only be rerolled once!
Soft armor is fashioned from animal skins or plant fiber. This armor is primitive, affordable, lightweight and bulky. Soft armor is vulnerable to fire & cutting weapons. This is the default armor type for birds, plants and mammals. Soft armor may be worn by any class except magic users.
Flexible armor consists of over-lapping steel scales or interwoven metal links designed to protect the torso and arms; an iron helmet will often accompany a suit of flexible armor. Characters usually wear leather gloves and sturdy boots with this armor. Flexible armor is vulnerable to acid & piercing weapons. This is the default armor for most reptiles and sea monsters. This armor is usable by fighters, barbarians, rangers, drifters and priests.
Rigid armor consists of custom fitted plates, attached with leather straps designed to protect most of the body. A sturdy helm usually accompanies this armor. This armor is cast in bronze, iron or steel from molds. This is the default armor type for most insects, crustaceans and dragons; rigid armor is vulnerable to cold, electricity & blunt weapons. Fighters, priests, clerics and heralds may use rigid armor.
In the above illustration by M Brook; the wise minotaur put his axe down in order to pound the snot out of the hoplite in rigid armor. Likewise, the Greek warrior selects his kopis (S) over the javelin (P) as a soft target (minotaur) is vulnerable to the cutting age of his curved sword.