In considering how to integrate Chainmail combat into an OSR campaign, two prevailing theories presented themselves: first, the most common, was the use of the d6-driven dice pool from troop combat in lieu of d20 rolls; second was the use of the 2d6 man-to-man table in lieu of the d20 roll: retaining attack progression and damage dice of the preferred edition. But - if attempting to engage with a concurrent mechanism - as detailed in the Hero entry - why not both?
So I took an afternoon to compare the probability curve of 2d6 target values
and translate them over to 1d20 - rounding for closeness - including an
easy-reference calculation for bonuses and penalties: what +1 on 2d6 meant for
the 1d20 target, retaining the same curve. Originally included as almost an
appendix in
the WW&W Players' Guide alpha, I present it below for easy access for anyone interested:
2d6 on 1d20
| With Penalty | Original Target | With Bonus | |||||
|---|---|---|---|---|---|---|---|
| -3 | -2 | -1 | +1 | +2 | +3 | ||
|
4 |
3 |
2* |
2 |
(1) | 1 |
1 |
1 |
|
7 |
4 |
3 |
3 |
(2*) | 1 |
1 |
1 |
|
9 |
7 |
4 |
4 |
(3) |
2* |
1 |
1 |
| 13 |
9 |
7 |
5 |
(4) |
3 |
2* | 1 |
| 15 |
13 |
9 |
6 |
(7) |
4 |
3 |
2* |
| 18 |
15 |
13 |
7 |
(9) |
7 |
4 |
3 |
| 19 |
18 |
15 |
8 |
(13) |
9 |
7 |
4 |
| 20^ |
19 |
18 |
9 |
(15) |
13 |
9 |
7 |
|
~ |
20^ |
19 |
10 |
(18) |
15 |
13 |
9 |
|
~ |
~ | 20^ |
11 |
(19) |
18 |
15 |
13 |
|
~ |
~ |
~ |
12 | (20^) |
19 |
18 |
15 |
In order to more closely (albeit not perfectly) align with the probability of success on 2d6:
- Target numbers marked with an asterisk (*) allow, on failure, a follow up re-roll against a target number of 9. If the roll against 9 succeeds, the roll succeeds.
-
Target numbers marked with a carat (^) require, on success, a follow up
confirmation roll against a target number of 9. If the roll against 9 fails,
the roll fails.
To arrive at these numbers, I did a simple tabulation for the probability of success to meet or beat a number on 2d6 for each of the possible results: 2 through 12. For example, in order to hit an 8 or higher - the requirement to hit a man with a shield when using a sword - there are 15 different combinations of dice: 15 out of 36 total results in a 41.6% chance of success - rounding to 40%, this lines up with a 13 or better on 1d20: rinse, wash, repeat. The 2 and the 12 - specifically - have a follow up roll, representing the 2.7%, 1-in-36 chance of not rounding "fairly" to either 0 or 5%.
The original intent of the matrix was to provide quick reference and allow for dice-pooling the d20 in tandem with a 0e character's fighting capability: so, a Hero who fights as 4 men would roll 4d20, comparing their chance of success against the success chance defined above rather than against the Alternative Combat System matrix. This made weapon choice much more significant, mathematically - a Hero on Hero action in troop combat, "Armored" versus "Armored", could be reduced from an almost impossible 1-in-1,296 chance to roll four simultaneous sixes to a rare, but possible 9% chance, rolling four 9s or better on 4d20 with a two-handed sword. Still a far cry from the 41.6% chance - a roll in excess of 7 (so, 8 or above - coincidentally the same as our sword against shield example) on 2d6 - presented for a Hero to defeat a Hero on the Fantasy Combat table - but still feasible.
Having delved deeper into the game and come to understand Fantasy Combat, I had not proceeded with the d20-dice-pool solution by default: however the math here remains - and hopefully it can find a use in your home brewing.
Delve on!
Open license artwork taken from Pixabay. Public domain art taken from OldBookIllustrations.com. Attribution in alt text.
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