Thanks again, squid830.
According to this formula, the Damage Threshold
is applied after
the ammo's Damage multiplier. This on its own seems to cripple FMJ/AP rounds, since JHP rounds have a much greater ammo Damage multiplier.
ND = net damage value
RD = random damage value produced from weapons hit damage range
RB = ranged bonus (RB=0 unless the player has Bonus Ranged Damage perk)
X = ammo damage multiplier
Y = ammo damage divisor
CM = critical hit damage multiplier (if no critical hit then CM=2, otherwise assigned value from critical hit table)
CD = combat difficulty multiplier (Easy=75, Normal=100, Hard=125)
AI = 1 if critical hit which ignores armor, otherwise 0
ADT = armor damage threshold value
ADR = armor damage resistance value
RM = ammo resistance modifier (only value allowed to be negative or positive in the equation)
ND = ((RD+RB) × (X/Y) × (CM/2) × (CD/100) - ADT/max(5*AI,1)) × (100 - max((ADR/max(5*AI,1) + RM),0) / 100
ND then rounded to nearest whole number
Cool. Thanks for recommending that, I may check that out at some point.
What do you mean when you say AP ammo is broken?
As in, they messed up something with the damage calculation formula, with the end result being that AP ammo is actually less effective than the equivalent HP ammo. See "Incosistency over effectiveness" section here: http://fallout.wikia.com/wiki/Armor_piercing
Just one of the many bugs of F2 (or a "design mistake" according to the Fallout wiki). Either way, RP (or the related unofficial patch without the RP content) should fix it, so that it functions properly. Or choose a different ammo mod (RP gives three options alone from memory).
That explains a lot. I've been running a few calculations (based off how I guessed the damage formula might work, I was quite close) and FMJ/AP rounds seem inferior to JHP rounds against every armor type I've found so far. This just confirms it.
Unfortunately I've yet to find one that fixes the issue with laser weapons. By which I mean, when you're first told about these "magical" weapons, they seem so awesome, able to cut through leather armor with ease. Turns out, almost any (ballistic) weapon is better than most laser weapons. The only possible exceptions are one or two heavy weapons. But to be fair this is more likely an issue with the armors in the game as opposed to the ammo - almost every armour has a higher DR against lasers than conventional weapons, for some reason - despite lasers generally not having higher damage output.
That's an issue in Fallout 1 as well.
Once you reach Metal Armor, every armor (thus far for me) has VERY high Laser DR.