I'm not a fan of ascending armor class. Too much emphasis on high numbers and number-jiggling.
And I'm not a fan of percentile systems. Too fine a granularity for me.
So, of course, after reading Randall's post that mentioned a percentile combat system with AAC, I thought of a way to do this. Haven't read the magazine article, so Randall will have to tell me whether I've accidentally copied the system he read about. Otherwise, this is free to anyone who cares about such things.
An unarmored target is AC 50.
Light (leather) armor adds +10.
Metal/hard armor adds +20 or +30, depending on whether the metallic bits are small or large. Halve the value if it's rusty.
A shield adds +5. Optionally, you can buy a +10 tower shield.
A simple leather cap is assumed to be included in any armor. A metal cap/open helm adds +5, a full helm +10.
Roll percentile dice and add your hit points to the result. If it's higher than the AC, you hit.
Ranged attacks add Dex, but a moving target adds Move to AC.
Opponents who chose to do nothing but dodge add their Dex to their AC.
The larger point differences of a percentile AC system means that you can add armor degradation. Every 00 rolled subtracts 1 point permanently from the target's AC. This happens after the test to hit, and 00 isn't an automatic hit, so super-high AC means you might take a hit that does no damage to you, but it slowly ruins your armor. The defender can pick which piece (shield, helm, body armor) is affected.
When you find or buy armor, on the first attack, the GM determines the armor quality: take the first digit of the attack roll and subtract the second digit to get a +/- 1 to 9 modifier to the armor's quality.