Boss zombies take 0.8 damage of base value
hunting_rifle&sniper_millitary: 114, 360 to head, 67 to leg
pistol_magnum: 97, 249 to head, 58 to leg
pistol: 44, 140 to head, 26 to leg
pumpshotgun: 300
shotgun_chrome: 303
autoshotgun: 302
shotgun_spas: 306
Melees: 375, 250 for witch, 5% tanks health, 487 charger
rifle: 41, 131 to head, 24 to leg
rifle_desert: 54 (per bullet), 175 to head, 32 to leg (per bullet)
AK-47: 72, 231 to head, 72 to leg
smg_silenced: 30, 99 to head, 18 to leg
smg: 24, 78 to head, 24 to leg
rifle_m60: 62, 199 to head, 37 to leg
grenade_launcher: 400 (1,200 for tank)
propanetank: 25
oxygentank: 25
pipe_bomb: 25
chainsaw: 1/ms
AWP: 143, 249 to head, 86 to leg
Sniper_scout: 131, 78 to leg, 420 to head
mp5: 31, 102 to head, 19 to leg
sg552: 41, 131 to head, 24 to leg

Damage drop-off: f=0.5 weapon damage

shotgun_chrome

• Has 8 pellets
  
• Has better accuracy than pumpshotgun
  
• 37 damage per pellet

pumpshotgun

• Has 10 pellets
  
• Has less accuracy than shotgun_chrome, but scatters for more zombies.
  
• 30 damage per pellet

shotgun_spas

• Has 9 pellets
  
• Has better accuracy than autoshotgun
  
• 34 damage per pellet

autoshotgun

• Has 11 pellets
  
• Has less accuracy than shotgun_spas, but scatters for more zombies.
  
• 27 damage per pellet

• Auto shotguns do 85% damage to tanks in L4D2.
  
• Auto shotguns do 75% damage to tanks in versus in L4D1
  
• shotgun_chrome and pumpshotgun can only do a maximum of 240 damage to tank.

• Shotgun pellets do 500% damage if you are within 100 units [2.5 meters] of common infected or a witch
  
• The witch and common infected only receive 75% damage on hard mode and 50% on expert, unless it's a head shot. If you're crowning witch aim for head and make sure all pellets hit.
  
• Headshots are always an instant kill on common infected.

• Bullets do 50% damage if they're shooting through something or drop off range
• Smokers tongue has 100 health
• The smoker will let go if he takes 50 damage
• Laser sights spread factor f=0.4 = 2.5 times more accurate
• Crouching doubles accuracy (I might be wrong, but I'm 95% sure it's correct)
• Explosive rounds do 200% damage
• Explosive rounds do 400% damage for shotguns
• Incendiary rounds burn for 4 seconds
• Fire does 40 damage per second
• Common infected can see and hear you at 500 inches away (41 ft || 12.5 meters)
• The tanks' rock has 50 health
• Boomer splat radius is 200 inches (16.7 feet || 5 meters)
• Boomer can puke 300 inches (25 feet || 7.62 meters)
• Smokers tongue can go 750 inches (62.5 feet || 19 meters)
• A Smoker must wait 15 seconds if he misses you
• A Smoker must wait 20 seconds if he hits you
• A Tank will swing if he gets within 50 inches of you (5 feet || 1.5 meters)
• A Tank can hit you from 56 inches away (5.5 feet || 1.67 meters)
• A Tank can only attack once every 1.5 seconds (that's 1,500 damage with the chainsaw)
• Witch threat hostile range 600 inches (25 feet || 7.62 meters)
• Witch threat normal range 300 inches (12.5 feet || 3.81 meters)
• Witch berserk range 200 inches (15 feet || 4.57 meters)
• Witch attack range 60 inches (5 feet || 1.5 meters)
• Flashlight can alert zombies from 400 inches away (30 feet || 9 meters)
• The size of a mob must be 10 to notify you
• Mob size is 30 zombies, mega mobs are 50 zombies
• Mobs at the end finale are 20 zombies
• Special infected can spawn every 45 seconds
• Common can respawn after 10 seconds
• Special infected can respawn after 10 seconds during finale
• There is a 75% change of tank and witch spawning per mission
• There is a 10% chance of witch or tank spawning during last mission
• Chances of a tank or witch appearing on first mission is 30%
• Zombie mobs spawn every 90-180 seconds
• Gas cans/barrels/etc have 20 health
• Explosions do damage from 400 inches away (30 feet || 9 meters)
• You lose 1 [temporary] health every 3 seconds
• You lose 3 health every second when incapacitated, unless everyone is, then it would be 12
• Mega-mob minimum/maximum spawn interval 7 minutes and 15 minutes
• Spawn density of items 6.48 items/100 yards
• Common infected vision range = 40 ft || 12 meters
• Common infected alert range = 80 ft || 24 meters
• Common infected max range from survivors = 250 ft || 76 meters
• Tank can attack every 1.5 seconds
• Tank has to be at least 250 inches (20.8 ft || 6.35 m) before capable of throwing debris
(Good for staying close while spamming shotgun)
• Zombie claw force is 240, and tank throw force is 800; Survivor shove force is 300, pushing objects is 25
• Zombie swing duration 0.2 seconds
• Explosion force is 2,000
• Falling more than 16.3 ft (4.98 m) will result in damage (velocity=560)
• Falling from 27 ft (8.2 m) will result in death (velocity=720)
• Being pulled by smoker reduces accuracy by 13.3%
• Being incapacitated reduces accuracy by 40%