Choppy Aim Script?

I am scripting a gun script, I am making it so the gun follows the mouse in first person. I have the basics but it is extremely choppy and I have no idea what the problem is.

local player = game.Players.LocalPlayer
wait(.5)
OFFSET = Vector3.new(0, 1, 1)
local body = player.Character
local mouse = player:GetMouse()
r = false
--Aim Part--
function onmove()
    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)
    if body.Torso:FindFirstChild("RightArmWeld") ~= nil
        then
        if r == true
            then
            a = 0
            local dif = body.Head.CFrame:toObjectSpace(script.Parent.Parent.Handle.CFrame).p + OFFSET
            body.Torso.RightArmWeld.C1 = CFrame.new(dif)
        end
        new = (mouse.Hit.p - mouse.Origin.p).unit.y
        x = -1.3
        y = .5
        z = .5
        body.Torso:FindFirstChild("RightArmWeld").C1 = CFrame.new(x,y,z)*CFrame.Angles(-math.asin((mouse.Hit.p - mouse.Origin.p).unit.y)-1.7,0,0)
    end
end
--
function ondown()
    r = true
end
function onup()
    r = false
end
mouse.Move:connect(onmove)
mouse.Button2Down:connect(ondown)
mouse.Button2Up:connect(onup)