You’re just a player-killer GM. :-)

I haven’t looked at GURPS in a long time. By the time I started looking into it there were simply too many peripheral sourcebooks that the folks I was gaming at wanted to use… and the advantages/disadvantages system seemed pretty susceptible to twinking, so I never actually played it.

Earthdawn, on the other hand, had something similar. Each character had two stats pertinent to armor and such, one was the the degree to which the armor would absorb damage, the other was the degree to which the character could avoid being hit. The first one would improve based upon armor worn, the second would improve as a part of character advancement (or magic).

Earthdawn had a built-in mechanism by which an “armor-defeating blow” could be dealt, basically bypassing the armor value entirely. This only happened when the attack roll was exceptionally high. Of course, Earthdawn has a variable-dice system that makes the probabilities slide around significantly during character advancement, so I’d have to sit down with some scratch paper, a calculator, a PHB and the Earthdawn rulebook to properly compare the systems (and alas, I don’t have an Earthdawn of my own).

But back to GURPS: Though not intimately familiar with GURPS (I read the core book about 10 or 12 years ago) I do like the splitting of armor value. With some hammering out, all of this may end up in my house rules for my D&D campaign, but that’ll have to wait until I kill off my current party (and get these ideas straightened out a bit).

I suspect that to make this work, there’d need to be a couple of different transformation algorithms for the existing equipment and character stats: The effect of armor for damage reduction, the effect of shields, the effect of which types of magic (deflection bonus to AC, luck bonus to AC, circumstance bonus to AC, etc)… It may end up becoming more complicated than would be of any use.

For my second thought – I’m a big fan of GURPS. In GURPS, armor has two stats, Passive Defense (PD) and Damage Resistance (DR). PD is used as a bonus to defense rolls (dodge, block or parry) as a mechanic to represent the chance that a blow will glance off the armor. DR is used to subtract hits from a damage roll. You could easily adapt the PD stat to effect AC as the current system does, but at a lower number and have the DR stat you propose.

One main thing to note about GURPS: characters only get the PD bonus for the top-most layer of armor (DR is cumulative, but the blow will only glance off the top layer) with the general exception that basic clothing (which has a PD of 0) doesn’t count as the top layer for this rule. There’s other factors, but then this “reply” will turn into a post detailing the GURPS combat system.

I could start spouting numbers and stats, but GURPS is a 3d6 system, so adding 1 to a target number (low is good in GURPS for skill and other success rolls) isn’t going to result in a linear increase in chance. I could present you with a statistical breakdown using baseline characters via email, if you are interested. I’m not sure if you’re familiar with GURPS or not – hopefully this post won’t be a waste of your time or space.