Simple own damage system.

SERVERSIDE:
addEventHandler("onPlayerSpawn", root,
    function()
        setElementData(source, "hp", 100)
    end
)

function setElementHealthEx(element, health, attacker, weapon, bodypart)
    if getElementType(element) == "ped" then
        setElementData(element, "hp", health)
        if hp <= 0 then
            killPed(element, attacker, weapon, bodypart, false)
        end
    else setElementHealth(element, health)
end

function killPedEx(ped, attacker, weapon, bodypart, stealth)
    killPed(ped, attacker, weapon, bodypart, stealth)
end
addEvent("killPedEx", true)
addEventHandler("killPedEx", root, killPedEx)

CLIENTSIDE:
function setElementHealthEx(element, health, attacker, weapon, bodypart)
    if getElementType(element) == "ped" then
        setElementData(element, "hp", health)
        if hp <= 0 then
            triggerServerEvent("killPedEx", root, element, attacker, weapon, bodypart, false)
        end
    else setElementHealth(element, health)
end

function damageFunc(attacker, weapon, bodypart, loss)
    cancelEvent()
    setElementData(source, "hp", getElementHealth(source) - loss)
    setElementHealthEx(source, getElementHealth(source) - loss, attacker, weapon, bodypart)
end
addEventHandler("onClientPlayerDamage", localPlayer, damageFunc)
addEventHandler("onClientPedDamage", root, damageFunc)