Fixing Rendering Problms?

I am making a gun that points towards your mouse in first person. It works perfectly besides the fact that it seems the guns lagging really bad :d. I tried renderstepped and it seems nothing happened, heres the scripts, thanks if you help!

heres the gun if you want to see the lag http://www.roblox.com/Border-Conflict-place?id=180698731

local player = game.Players.LocalPlayer
local body = player.Character
local mouse = player:GetMouse()

while true do
    Game:GetService("RunService").RenderStepped:wait()
    body.Torso.Neck.C1 = CFrame.new()
    body.Torso.Neck.C0 = CFrame.new(0, 1.5, 0) * CFrame.Angles(math.asin((mouse.Hit.p - mouse.Origin.p).unit.y), 0, 0)
        xangle = -math.asin((mouse.Hit.p - mouse.Origin.p).unit.y)-1.7
        new = math.asin((mouse.Hit.p - mouse.Origin.p).unit.y)
        if new >0
            then
        script.Parent.Parent.GripPos = Vector3.new(0,new*1,-new*1.2-.4)
        else if new <0
            then
            script.Parent.Parent.GripPos = Vector3.new(0,0,-new*.9-.4)
        end
        end
        body.Torso:FindFirstChild("RightArmWeld").C1 = CFrame.new(-1.5,.5,.5)*CFrame.Angles(xangle,0,0)
    Game:GetService("RunService").RenderStepped:wait()
    end