But . . . I wondered to myself if there was a way to turn some sort of real-world number into D&D damage output.
I know, I know. Why would I ever do such a thing? I had noted (complained, really) that a 9mm was 2d6, and the mighty .50BMG was but 2d12.
So . . . I whipped out solver, and it turns out if you use the energy of the bullet, and only the energy of the bullet, if you use 4 * Log (Base 5) Energy you get a number that might just equate to the maximum damage you can roll on the dice. It compresses the scale even further than the usual result, but it's not insane.
|Cartridge Name||D&D Damage?||Roughly|
|180gr 10mm Auto||16||2d8|
|12 Gauge Shotgun Slug||20||2d10|
|150gr NATO 7.62x51mm||20||2d10|
|.300 Win Mag||21||2d10+1|
|.338 Lapua Magnum||22||2d10+2|
|16" Naval gun||49||8d6+1|
Show the Work
How did I do it?
I tried to make a .22LR 8 points (2d4), a 9mm 12 points (2d6), and a .50BMG 24 points. I used a formula to set a quantity of D = A * logB(Energy). I squared the difference and normalized it to the target squared . . . so (D-T)^2 / T^2. I also weighted the results, so the .22LR got 1000x the figured sum, the 9mm got 4000x, and the BMG got 9000x. That was to force Solver (in Excel) to give more weight to making the .50BMG 2d12 or 24 points. The energies I used were 130J for the .22LR, 585J for the 9mm, and 14,700 for the .50BMG, which assumes a man-portable 32" barrel instead of the 43" bbl on the machinegun (which is about 16,000J).
Solver gave an exact figure of A = 3.88 and B of 5.1. But setting A=4 and B= 5 is actually better at fitting the BMG, and puts the .22LR at the 2d6 value above. Given the energy involved, that's probably as good as the d20 modern values.
When converting max damage to dice, I always use the largest dice I can, but don't allow subtraction. So 19 points isn't 2d10-1, but rather 2d8+3. That's a quirk of mine. You can certainly convert any way you like, and 39 points could be 4d8+5, 4d10-1, or 3d12+3 easily enough. Heck, have at it and make it 9d4+3, and the 16" Naval Gun 12d4+1 to keep the minimum damage high.
Note that the Naval Gun is just the kinetic energy. I haven't yet figured out how to rate the explosion of 150 lbs. of high explosive inside about 2,000lbs of metal.
Bah! The Damages are Too High!
A comment on G+ noted that 3e humans only have 4 HP, which is a fair point. If you wanted purposefully lower numbers, then here are some nudges/hacks, as well as my line of thought.
I based them off of d20 Modern's list, where a 9mm was 2d6 and a .50BMG was 2d12. The math forced the 9mm to 2d8 and put the .22LR, which I tried to make about 2d4, into 2d6.
In 5e, at least, a 1st level fighter is going to start with at least 10 HP, and you get a DEX bonus to the 1d6 or 1d8 base damage of a short or longbow, respectively. So from that perspective, 2d6 (ish) or 2d8 for a pistol is the equivalent, on the average of 1d6+3.5 and 1d8+4.5 for damage, neither of which is out of line for d20 Modern or 5e, at least.
If you lower the values to make them work for low level characters, you have the opposite problem - a high level fighter can shrug off a burst of .50BMG unless you invoke the harshest of harsh wounds rule where if you take more HP than your CON, you save or die (that's a suggested threshold - the harshest one - from the d20 Modern SRD).
If you force the .22LR down closer to a shortbow, the formula becomes something like 2*log(base4) Energy. That makes a .22LR 1d6+1, a 9mm about 1d8+1, a 5.56mm 1d10+1, 7.62mmNATO 1d12, and a .50BMG 1d12+2.
This gives fewer categories of damage
- 1d6+1 for .22LR
- 1d8 for .380 ACP
- 1d8+1 for PDW rounds and all normal military pistols (.45 ACP, 9mm, 10mm, .40S&W)
- 1d10 for magnum pistols (.357M, .44M) and lower-powered assault rifles (4.73x33mmCLS, 5.45x39mm)
- 1d10+1 for standard military assault rifles (5.56, 6.8SPC, 7.62x39mm, 6.5 Grendel)
- 1d12 for battle rifles and sniper rifles from .308 to .338 Win Mag
- 1d12+1 for .338 Lapua or .416 Rigby
- 1d12+2 for .50BMG