I only really started regularly playing D&D with 3rd edition but was curious as to what range of AC's classic D&D (2e and earlier) were possible for both monsters and player characters as well as the range possible with newer incarnations in the OSR/OSE genre.  Was the range more restricted than D&D 4e and current PF2?  More narrow that the consciously narrowed 5e?  While I bought books during 2nd edition, I only played two very short one on one games with an equally clueless DM friend but I have a vague memory of charts that go to -10 (in the old THACO system) for adult dragons and such but no idea how common the spread was.  The chart at the link below says a character in full plate and shield has an AC0 in 1e/2e which would be the equivalent of 20 in the modern ascending AC mechanic but I have no idea how common other buffs like magic items, class/racial abilities, etc further bumped that. 

Is there a difference in the spread between classic D&D and modern OSR stuff in that regard?  Is it generally easier now to hit equivalent targets due to bonus point inflation over the decades/editions or was/is it harder in older style rules in general to land a hit at the extremes?   Thanks in advance for any info on this topic.

https://dungeonsdragons.fandom.com/wiki/Armor_class

The longest OSR campaign I've played in was for Hyperborea, which uses THAC0, and I recall ACs ranging from 8 down to about -4 or -5. Monster AC might go lower, but the VTT system couldn't calculate a hit of better than -4, so it's probably just as well we didn't get to that level. I think in most ascending AC games the maximum you can get is about 25, with max dex and enchanted armor, but the highest you're likely to see on a player is probably around 22. I don't think most OSR games allow for the 30+ AC monstrosity builds you could go for in 3.5.

Thanks!  Did the players have to optimize to get down that low (the equivalent of 24-25 AC in modern D&D)?   I'm unclear on how that works in OSR style games (which admittedly is a broad category in and of itself so may have different answers).   I've seen some games with random charts you roll on when you level up that might have an AC boost but don't know if you can pick rolls or abilities/feats/boons/whatever to get it.

Not really. Full plate, a shield and a +1 dex bonus (all very reasonable for a fighter) gets you down to a -2 AC by itself (in Hyperborea 3ed, which is the book I have handy), and by mid-level you can probably count on having some spells or magic equipment to make up the last couple of points. By around level 6 even my thief had an AC below 0.

Armor class is probably the element of D&D which has changed the least over the editions, at least as far as the underlying math goes. The biggest change came with 3rd edition when they changed how the attribute modifiers worked. That meant most characters were going to have a higher dex bonus to armor, which forced them to make it so that armor limited your max dex bonus (which isn't generally true in old school).

The practical effect of that when you compare 5e to OSR, is that the general range of PC armor classes is about the same. The only change I see is that it's a little harder for a fighter to get up to that 24-25 ascending AC equivalent in 5e, but much easier for a non-fighter to get into the high teens. They've kind of compressed things to where barring major magic items, most characters are going to have an AC of between 15 and 20.

Quote from: ForgottenF on May 04, 2024, 12:03:38 AMNot really. Full plate, a shield and a +1 dex bonus (all very reasonable for a fighter) gets you down to a -2 AC by itself (in Hyperborea 3ed, which is the book I have handy), and by mid-level you can probably count on having some spells or magic equipment to make up the last couple of points. By around level 6 even my thief had an AC below 0.

Armor class is probably the element of D&D which has changed the least over the editions, at least as far as the underlying math goes. The biggest change came with 3rd edition when they changed how the attribute modifiers worked. That meant most characters were going to have a higher dex bonus to armor, which forced them to make it so that armor limited your max dex bonus (which isn't generally true in old school).

The practical effect of that when you compare 5e to OSR, is that the general range of PC armor classes is about the same. The only change I see is that it's a little harder for a fighter to get up to that 24-25 ascending AC equivalent in 5e, but much easier for a non-fighter to get into the high teens. They've kind of compressed things to where barring major magic items, most characters are going to have an AC of between 15 and 20.

Interesting as I wouldn't have expected that.  With the typical mechanic of simply rolling 3d6 instead of point buy and not having chooseable feats typically that may selectively boost things, I'd have assumed the average AC to be lower (though the outliers of the tiny percentage of players who actually legitimately roll 16+ for dex being the obvious exception).   I also didn't realize there wasn't a cap (at least in Hyperborea) on dex for the heaviest armors.

In my experience, it's a minority of OSR tables that actually play 3d6-down-the-line. Systems vary, and I don't see the modern "4d6 drop the lowest" very often in OSR. The system I use for my game is "1d6+1d4+6 down the line", in order to produce middling scores. I think that Hyperborea campaign did "roll 3d6 down the line three times, and then pick from the three stat arrays generated".

I think in some OSR games you only need a 15 to get a +2 attribute bonus as well.

Classic D&D was quite varied.  BECMI D&D had ACs that ranged from 9 to at least -15

What got to -15 if you don't mind me asking?   Heavily armored monsters like dragons/earth elementals/golems only or even player characters?   Did you have the option in BECMI to boost it further or was it dependent on a random roll on a level up upgrade table?

If you look at the pre-generated characters in old modules, you'll see that negative ACs were very common. For example, in D1, the sample characters are all around 10th level and their ACs listed are: -4, -3, -2, 1, -3, -1, 0, -3, and -2.

In S1, all the characters have magical armor or rings/cloaks of protection and all fighters have magical shields.

Thanks and that's a good point that I didn't mention in the original post in that the expected AC range in a classic D&D/OSR style game will be dependent on the level in addition to just the general core ruleset.  I'm not familiar with the D1/S1 nomenclature so will have to look that up tonight.