Weapons Increase Armor Class?

I had a little notion this morning about a different way to run combat in d20-esque games. This is a departure from normal combat, but can be done pretty easily.

Here's the plan:

Damage is not based on the weapon, but on the success at the attack roll. There are a variety of ways you can do this. The most simple would be something like:

  Roll < AC = no damage (obviously)

  Roll = AC = 1d3 damage ('tis but a scratch)

  Roll = AC +1 = 1d4 damage

  Roll = AC +2 to +3 = 1d6 damage

  Roll = AC +4 to +5 = 1d8 damage

  Roll = AC +6 to +7 = 1d10 damage

  Roll = AC +8 to +9 = 2d6 damage

And so on, adding +1d6 to damage each time. You can adjust the ranges and damages to suit yourself, of course.

So what good is a weapon in this system?

Weapons in this system would add to AC based on their length. If your weapon is longer than your opponent's weapon, it is harder for the opponent to get close and strike. We could say for every foot difference in the length of the weapons, you get a +1 to AC, up to a max. of +3. We don't want the weapon's length to completely overshadow actual armor in the AC calculation. We might also want to factor in the size of the combatants, with maybe every 2' of height (or length) equaling a +1 bump to AC, up to +3. The combination of height and weapon length, therefore, would give a max. bump to AC of +6.

Weapons also add to damage based on their stated damage in the rule books, as follows:

  1 to 1d3 damage = +0 to damage
  1d4 damage = +1 to damage
  1d4+1 and 1d6 damage = +2 to damage
  1d6+1, 1d8 and 2d4 damage = +3 to damage
  1d10 damage = +4 to damage
  1d12 and 2d6 damage = +5 to damage

Strength also adds to damage, as normal, and dexterity adds to AC.

Example Combat: Halfling Fighter vs. Ogre
We'll pit two combatants against one another.

The first is a 5th level halfling fighter with a +1 Dex bonus and platemail and a short sword. The halfling (using Blood & Treasure rules) has a total bonus to hit of +5 (for level, no strength bonus). Her armor class is 18 (+7 armor, +1 Dex). She has 28 hit points.

The second is a 4 HD ogre with no armor and a spear. The ogre has a +4 bonus to hit (based on his HD) and AC 16. He has 17 hit points.

We'll impose the following adjustments, based on the above rules:

The ogre is 8 feet tall, vs. the halfling's 3 feet of height. This is a 4' difference, so the ogre gets a +2 bonus to AC. The ogre is also using a 6-foot long spear, vs. the halfling's 3-foot long short sword, which gives the ogre another +3 bonus to AC. This gives the ogre a total AC of 21 in this fight.

The halfling's short sword gives her a +2 bonus to damage. The ogre's spear gives him the same.

We'll give the halfling initiative ... her first attack roll is a 17, +5 for her attack bonus, equals 22. This beats the ogre's AC by 1 point, and thus scores 1d4+2 damage. In this case, 4 points of damage. This reduces the ogre to 13 hit points.

The ogre rolls a 19+4 = 23. This beats the halfling's AC by 5, which translates into 1d8+2 damage. The ogre rolls 5 points of damage, reducing the halfling to 23 hit points.

In the next round, the halfling rolls a 23, beating the ogre's AC by 2, and scoring 1d6+2 damage. The halfling rolls another 4 points of damage, reducing the ogre to 9 hit points.

The ogre responds with an attack roll of 5, missing the halfling.

And so on ... it is likely that the halfling will win the fight, though the ogre has a slightly better chance to score more damage, and he is slightly harder to hit.

Final Thoughts
I don't think this is a better way to run combat, just different. If it has any advantage, it is that it takes into account the reach of a creature and weapon in a way that normal combat rules do not. Further development of the idea might lead to a better system, or might suggest alterations to the existing combat system that might make it better.