Rescuing a Rob Conley Comment from Obscurity

Posted on Grognardia by Rob Conley:

The Chainmail tables are meant to capture the penetration difference. The assumption was if the blow manages to penetrate it is going to kill the individual. Consider each blow in chainmail to do 1 pt of damage and normal men have 1 hp.

OD&D changes this so that damage is now a 1d6 and normal men start off with 1d6 hit points. This is to represent the variability of people and the vagaries of combat.

(Waxing Gygas me thinks)

Then in Greyhawk come the realization that some weapons are better able to hurt people if they hit. The force behind the two-handed sword is way more than a one-hander. The different types of trauma, (slash, stab, blunt) are just arbitrarily factored in.

Later on as RPGs grew more complex some start making the distinction. (GURPS, Rolemaster, Harnmaster, etc).

Separate but parallel is the need to fold in all the non-armor modifiers particularly for monsters. In the beginning AC was a straight forward representation of armor types but became divorced from the under lying armor system to become a scale measuring how are things are to hit. D20 take this to it's logical conclusions' giving armor a modifier

This whole disconnect is why in AD&D the weapon vs AC says to look at what the guy is wearing not his numerical AC.

If you want to use modifiers versus AC and not violate IP what you should do is return the chainmail roots and just list the modifiers for each weapons and include any notes for particular monsters.

You can derive the values from the chainmail table. For example (note I don't have chainmail in front of me so I making stuff up)

Longsword
+3 vs no armor
+2 vs leather
+1 vs chain
+0 vs plate
-2 vs Dragons
+1 vs Chimeras
+1 vs Trolls
+2 vs Purple Worms

You can get as complex or simple as you want as well as avoiding IP problems.