The key to surviving in gunfights is knowing how much damage you can take. The damage listed below is for body shots and does not count bleeding.

Handguns
R380: 15 damage
M1911: 25 damage
Magnum: 30 damage
M9: 19 damage

Rifles
AR15: 25 damage
AK47: 32 damage
Hunting Rifle: 65 damage

Shotgun
Shotgun: 1 shot kill at close range/no armour

Bows
Bow: 35 damage
Crossbow: 35 damage

Melee Weapons
Stick: 6 damage
Machete: 10 damage
Axe: 10 damage
Knife: 10 damage