Like many Authors, I tasked myself with trying to figure out how to assign damage values to ammunition that was not listed by the game manufacturer, in this case White Wolf. Some authors simply take their best guess and use educated guesses to place ammo in between the listed values. This usually works, depending on the authors knowledge. I tend to take a more mathematical approach that eliminates personal bias (see D20 Modern's love of the five Seven). These are the steps that I took.
First, I consulted with the New World of Darkness Armory supplement and found the damages for some common firearm rounds and compared them with the muzzle energy of the standard load.
White Wolf Damages
|.22 LR||1||100 ft*lbs|
|.25 ACP||1||75 ft*lbs|
|.32 ACP||1||129 ft*lbs|
|7.65 Tokarev||1||300 ft*lbs|
|5.7 mm FN||2||400 ft*lbs|
|.38 Special||2||176 ft*lbs|
|380 ACP||2||200 ft*lbs|
|9 mm||2||396 ft*lbs|
|.38 Super||2 (9 Again)||500 ft*lbs|
|.357 Magnum||3||583 ft*lbs|
|.357 SIG||2 (9 Again)||544 ft*lbs|
|.40 S&W||2 (9 Again)||524 ft*lbs|
|10 mm||3||680 ft*lbs|
|.45 ACP||3||495 ft*lbs|
|.44 Magnum||3||1100 ft*lbs|
|.45 Long Colt||3||497 ft*lbs|
|.454 Cassul||4||1955 ft*lbs|
|.50 AE||4||1661 ft*lbs|
|.500 S&W||4 (9 again)||2580 ft*lbs|
|5.54 mm Soviet||4||1045 ft*lbs|
|5.56 mm Nato||4||1460 ft*lbs|
|.270 Winchester||4||2786 ft*lbs|
|.30 Carbine||3 (9 Again)||1075 ft*lbs|
|.30 - .30||4||1920 ft*lbs|
|.300 Win Mag||4 (9 Again)||4187 ft*lbs|
|.308 Winchester (7.62 mm Nato)||4 (again)||2680 ft*lbs|
|7.62 x 39 mm||4||1762 ft*lbs|
|7.62 x 54 mm Soviet||4 (9 Again)||2910 ft*lbs|
|.30-06||4 (9 Again)||3076 ft*lbs|
|.375 H&H Mag||5||4697 ft*lbs|
|.460 Weatherby||5||7799 ft*lbs|
|.50 BMG||5 (8 Again)||13910 ft*lbs|
I found that the new dice rules (8 and above on a Die 10 are successes and 10s explode) gave every dice a 33% chance of success. If 9s and 10s get rerolled, there is a 37.5% chance of success. I then used these to figure out how likely (according to Whitewolf) the guns are to inflict a box of damage. (Damage rating times .333 or .375)
I plotted the Muzzle Energies versus the White Wolf Damage dots and got this graph.
I then had Excel try to best fit a Exponential equation to fit the White Wolf data. This curve is understandable because you get dimishing returns when using bigger and bigger weapons on a human size target. A .50 BMG will overpenetrate just about anything (human, werewolf or undead).
From there, I plugged in the muzzle energies from various rounds into the best fit equation and rounded to the nearest whole number. The numbers seem to fit WhitWolf's. I did try to plot the (9 again) values, but it gave me a lot more (9 again) values. I figure that (9 Again) and armor piercing values were generically assigned afterward to distinguish rounds that are assigned the same value, but are quite different from their neighboring rounds. These were added based on personal experience and ballistics data.