Armor and Damage Reduction

[Dimirag]

The attack roll is not an unmodified d20 as you modify it by your STR or DEX mod.

In Unisystem(R) system blunt weapons have better damage value compare to cutting/piercing, so they ignore most of the armor, but cutting/piercing weapons deal extra damage after they pierce through an armor...

There are lots of options to chose:
AC as a save that negates damage
AC as a save that transforms lethal damage to non-lethal damage (if using an alternate lethal-non-lethal damage system).
AC as a threshold against attacks or damage to determine lethal/non-lethal damage
and others...

A minimum damage would be of great help, or some other mechanism that makes that low damage attacks are still effective against really strong armors (if you use a separate pool of HP for non lethal damage you can rule that any damage that goes under the AC is suffered as non-lethal*).

*Non-Lethal HP -> Standard HP
*Lethal Damage -> Percentage of HP (instead of CON as monsters don't have CON values)...