Fallout: New Vegas Combat

Fallout: New Vegas has a combat system that is very similar to its predecessor, Fallout 3.

V.A.T.S.
 The Vault-Tec Assisted Targeting System returns to Fallout: New Vegas allowing the player to freeze combat and specifically target six different limbs at the cost of Action Points. It is mostly unchanged in principle from Fallout 3.

Changes

 * Every melee weapon can execute a special attack, which, however, requires having a Melee Weapons skill of at least 50.
 * Unarmed weapons gain Uppercut and Stomp special attacks at skill levels 50, and Cross at skill level 75. These attacks have an AP cost of 20 regardless of the weapon used.
 * Base melee/unarmed damage (except thrown melee weapons) dealt by the weapon is automatically doubled.
 * You take 75% damage in Vault-Tec Assisted Targeting System|V.A.T.S. instead of 10%. Dying in Vault-Tec Assisted Targeting System|V.A.T.S. is a very real possibility.
 * The V.A.T.S. critical chance bonus is 5% instead of 15%.
 * V.A.T.S. no longer inflicts additional weapon's durability damage on use.
 * Enemies are less aggressively slowed down; while all enemies move slower in V.A.T.S., those not actively targeted are not slowed nearly as dramatically.

Aim down sights
A new feature in Fallout: New Vegas allows the player character to aim down the iron sights of their firearm. As opposed to in Fallout 3 where the "aim down sights" was simply a zoom in feature to the side of the weapon. This reduces the weapon's sway (crouching also reduces sway).

Combat damage
Damage calculations that follow are not to be taken as 100% accurate. There are various exceptions in how certain modifiers get included (such as DT), so this is intended to be a general guide.

First, Dam needs to be calculated, where:
 * $$Dam=Dmg \times Skill \times Cond \times Power + Bonus$$


 * Dmg = Unmodified, base weapon damage, as seen on individual weapon pages.
 * Skill = A weapon skill modifier ranging from .5 to 1.
 * Cond = A weapon condition modifier, ranging from .5 to 1.5.
 * Power = For any Melee/Unarmed power attack or any Melee/Unarmed non-sneak Vault-Tec Assisted Targeting System|V.A.T.S. attack this is set to 2, otherwise 1.
 * Bonus = The player character's strength bonus (if using melee), unarmed bonus (if using unarmed), or 0.

Second, Melee/Unarmed special attack multiplier, critical damage (if a critical roll succeeded) and armor reduction are added in, where:
 * $$Dam_{adjusted1}=(Dam \times Special + isCrit \times CritDmg \times CritPerks) \times DR$$


 * $$DT_{adjusted}=max(0, DT \times AmmoDT_{mult} - AmmoDT)$$


 * $$Dam_{adjusted2}=max(Dam_{adjusted1}\times 0.2, Dam_{adjusted1} - DT_{adjusted})$$


 * Special = Melee/Unarmed V.A.T.S. Special Attack multiplier.
 * isCrit = 1 if a critical hit, otherwise 0.
 * CritDmg = Unmodified critical bonus damage, as seen on individual weapon pages.
 * CritPerks = Perks that multiply critical damage (Better Criticals, Stealth Girl, etc.) These usually stack multiplicatively, so Better Criticals and Just Lucky I'm Alive would result in 225% critical damage, instead of 200%.
 * DR = A number ranging from 1 to .15, representing the Damage resistance of the target.
 * DT = The Damage Threshold of the target. Note that DT cannot reduce damage (DR modified) below 20%.
 * AmmoDT_mult = Ammo DT multiplier (such as the x3 of HP ammo).
 * AmmoDT = Ammo DT reduction (such as the 15DT reduction of AP ammo). Note that it cannot reduce DT of the target below 0.

Finally, any other multiplicative modifiers are included, such as:
 * $$Final\ damage=Dam_{adjusted2} \times SA \times LM \times AM \times DM \times Perks \times Chems$$


 * SA = Sneak Attack multiplier: 2 if ranged, 5 if Melee/Unarmed.
 * LM = Location multiplier for ranged attacks. For example, most creatures with a head take 2x damage from headshots and ants take 0.5x damage to their legs.
 * AM = Ammo type damage multiplier (such as the x1.75 of HP ammo).
 * DM = Difficulty multiplier: 2 on very easy, 1 on normal difficulty, 0.5 on very hard.
 * Perks = Damage multipliers from perks such as Lord Death, Bloody Mess, Living Anatomy, etc. These usually stack multiplicatively as well, so Lord Death (rank 3) and Bloody Mess would be a 9.2% increase in damage instead of 9%.
 * Chems = Damage multipliers from chems such as Psycho, Slasher, etc.