Weapon Damage Modifier can be the way to go
Basically if you set it in 0.5 it will take double amount of bullets to kill someone. so if you set it to 2.0 it will double the damage of a gun that you want. if you set it to 0 your gun won’t do any damages
here is a basic example for doing it
Citizen.CreateThread(function()
while true do
SetWeaponDamageModifier('WEAPON_APPISTOL',2.0)
Citizen.Wait(0)
end
end)
i made custom Damage modifier for all of my guns in my last release ( military tdm gamemode )
in config file it looks like this
Config.CustomDamageMultipilier = true
Config.WeaponDamage = {
UnArmed = 0.5,
CombatPistol = 0.75,
SpecialCarbine = 0.75,
RPG =0.75,
SMG = 0.75,
Shotgun = 0.75,
Sniper = 0.75,
CarbineRifle = 0.75,
SmokeGrenade = 0.5
}
Main Code is this 
Citizen.CreateThread(function()
while true do
if Config.CustomDamageMultipilier then
SetWeaponDamageModifier(GetHashKey("WEAPON_UNARMED"),
Config.WeaponDamage.UnArmed)
SetWeaponDamageModifier(GetHashKey("WEAPON_COMBATPISTOL"),
Config.WeaponDamage.CombatPistol)
SetWeaponDamageModifier(GetHashKey("WEAPON_SPECIALCARBINE"),
Config.WeaponDamage.SpecialCarbine)
SetWeaponDamageModifier(GetHashKey("WEAPON_RPG"),
Config.WeaponDamage.RPG)
SetWeaponDamageModifier(GetHashKey("WEAPON_SMG"),
Config.WeaponDamage.SMG)
SetWeaponDamageModifier(GetHashKey("WEAPON_CARBINERIFLE"),
Config.WeaponDamage.CarbineRifle)
SetWeaponDamageModifier(GetHashKey("WEAPON_MARKSMANRIFLE"),
Config.WeaponDamage.Sniper)
SetWeaponDamageModifier(GetHashKey("WEAPON_ASSAULTSHOTGUN"),
Config.WeaponDamage.Shotgun)
SetWeaponDamageModifier(GetHashKey("WEAPON_SMOKEGRENADE"),
Config.WeaponDamage.SmokeGrenade)
end
Citizen.Wait(0)
end
end)
if you got any error using SetWeaponDamageModifier try to use the hash and invoke it instead of using the SetWeaponDamageModifier itself
here is a example for using hash instead of SetWeaponDamageModifier
Citizen.CreateThread(function()
while true do
if Config.CustomDamageMultipilier then
N_0x4757f00bc6323cfe(GetHashKey("Your Weapon"),
Damage)
end
Citizen.Wait(0)
end
end)
The Invoke Key For SetWeaponDamageModifier is 0x4757F00BC6323CFE