This script that should move my gun wherever my camera goes is not working, any help?

This gun script that is only supposed to have the gun face wherever my camera is keeps on moving me around really fast. The code is here:

local camera = game.Workspace.CurrentCamera
local humanoid = game.Players.LocalPlayer.CharacterAdded:Wait():WaitForChild("Humanoid")
local repWeapon = game.ReplicatedStorage:WaitForChild("P90")
local weapon = repWeapon:Clone()

local viewModel = game.ReplicatedStorage:WaitForChild("viewModel"):Clone()

weapon.Parent = viewModel
viewModel.Parent = camera

local joint = Instance.new("Motor6D")
joint.C0 = CFrame.new(1, -1.5, -2)
joint.Part0 = viewModel.Head
joint.Part1 = weapon.Handle
joint.Parent = viewModel.Head

local function onDeath()
	viewModel.Parent = nil
end

local function onUpdate(dt)
	viewModel.Head.CFrame = camera.CFrame
end

humanoid.Died:connect(onDeath)
game:GetService("RunService").RenderStepped:connect(onUpdate)