Fallout: New Vegas Combat

Combat Damage

 * DAM = Derived in-game statistic representing the power of a weapon. Not used in calculations
 * DMG = Unmodified weapon base damage. DAM is equal to DMG with a weapon at full repair, 100 weapon skill and no damage modifying perks
 * CRITDMG = Unmodified bonus damage added for critical strike on target
 * SA = Sneak Attack modifier adds +100% total damage
 * BC = Better Criticals modifier adds +50% critical damage
 * HS = Headshot modifier adds +100% total damage
 * DT = Damage Threshold of target
 * AM = Ammo type multiplier
 * DM = Difficulty multiplier. One on normal difficulty, 0.5 on very hard.
 * PERK_MULTIPLIERS = Other damage multipliers from perks such as Lord of Death, Bloody Mess and Living Anatomy

The damage formula is calculated as follows:
 * DAMAGE_TO_TARGET = (DMG+CRITDMGxBC-DT)xSAxHSxAMxDMxPERK_MULTIPLIERS

The main thing to note is that target's damage threshold is subtracted directly from base weapon damage before any multiplicative modifiers are applied.