I use armor as damage reduction in my game. Not terribly complex, simple as using the armor class as the damage reduction value. Playing for 8 months with it now, I haven’t had any issues with it (but the highest level any character has gotten in that time is 3rd, it’s kind of slow moving). But I think I will once levels start creeping a little higher.
See, I had the good fortune to be able to add another player recently,and in the process of explaining the armor thing, he asked if there were other ways to increase AC. I still use AC, it’s dex and shields which avoid hits, armor makes them less damaging. Which started me thinking, “Hmm… If AC is going to stay around 12-16 for most characters, BAB is going to become meaningless pretty quick.” So I thought some more and, as is my usual, I devised an elegant solution. Allow players to increase either BAB or a “class defense” bonus every time they would get an increase in BAB.
See, the reason it’s so elegant is 1) I don’t have to rewrite the class tables, 2) it provides another way to customize for the players, and 3) it keeps the balance of to-hit and AC aligned, while maintaining the damage reduction role of the armor.
I realize that keeping pace between to hit and AC will mean fewer attacks per round at higher levels, it also means there is an opportunity to unbalance characters, to focus either on hitting or attacking. Personality in combat through the rules.
But I think it all works. I’ve kind of intellectually taken issue with the idea of 4 effective attacks in the space of 6 seconds anyhow, so this will also have the effect of making that more realistic, and making combat even more deadly than it has been in my game.