Delta had a good post the other day about what he believes to be a big error in the weapon-vs-armor table present in the 1e DMG (and as far as I can tell, identical to the one in Supplement 1, Greyhawk, which I noted in passing).
I think Delta is correct, that the modifiers were just taken by looking at the difference between 8+ and the target number for each entry, which means that (for example) maces aren't particularly good against heavy armor, and that in general you get very un-Chainmail-like outcomes for a table nominally derived from Chainmail.
But Delta doesn't quite follow through to publishing a revised table. He asks at the end if that's something that people would like to see. And I was curious so I decided to have a stab at it myself.
First I converted each of the target numbers on 2d6 into a probability and then into a target number on d20.
|TN 2d6||% hit||% miss||TN d20|
Then I filled those d20 target numbers in for each weapon:
|d20 target numbers||No armor||Leather||Shield only||Leather
Finally, I converted those target numbers into modifiers relative to the baseline target number to hit that type of armor in Supplement 1 (10+ for No Armor, 12+ for Shield Only, 17+ for Plate+shield, etc)
|No armor||Leather||Shield only||Leather
This seems somewhat unnecessarily complicated, though, since you have to check both a modifier for the armor and then a modifier for the weapon. I rather like the big table of d20 target numbers - sum your adjustment from Str, magic weapons, and level, subtract for defender's magic armor and rings of protection, roll your d20, add your bonus, and look up in the table what you need to hit.
I don't know that these direct conversions by probability are actually reasonable within the context of balancing weapon choices for AD&D. The heavy weapons get some really big bonuses to hit, and they don't have the counterbalancing factors that they did in Chainmail's man-to-man combat system, where opponents using lighter weapons could parry or attack multiple times in a round against opponents using heavier weapons.