How can I rotate something welded to the player?

Code:

workspace.ChildAdded:Connect(function(obj)
    wait(1)
    if obj:FindFirstChild("Humanoid") then
        local gun = script.gun:Clone("Gun")
            gun.Parent = obj
        local weld = Instance.new("Weld")

        weld.Parent = gun
        weld.Part0 = gun
        weld.Part1 = obj:WaitForChild("Torso")

        weld.C0 = obj.Torso.CFrame + Vector3.new(0.6,0.4,0.6)
        weld.C1 = obj.Torso.CFrame

    gun.CFrame = gun.CFrame * CFrame.Angles(math.pi / 2, 0, 0)
    end
end)

Result: https://gyazo.com/bf7a240ac09dc69d0242af05f9b12462

Am I missing something obvious?

I'm new to CFrames. I just want the gun to be rotated so its facing down.