Why won't this animation/weld localscript work?

This localscript weld animation thing doesn't work when i walk but if i don't walk it works. Whats the problem? Anyone?

gun = script.Parent
Player = game.Players.LocalPlayer
la = Player.Character:FindFirstChild("Left Arm")
t = Player.Character:FindFirstChild("Torso")
rs = Player.Character.Torso:FindFirstChild("Right Shoulder")
ls = Player.Character.Torso:FindFirstChild("Left Shoulder")

local function weldBetween(a, b)
    local weld = Instance.new("Weld")
    weld.Part0 = a
    weld.Part1 = b
    weld.C0 = CFrame.new()
    weld.C1 = b.CFrame:inverse() * a.CFrame
    weld.Parent = a
    return weld;
end

function localequipped()
    weldBetween(la, gun.Handle)
    rs.C0 = rs.C0 *CFrame.new(0.5,1,0)
    ls.C0 = ls.C0 *CFrame.new(0,5,4.75)

end
gun.Equipped:connect(localequipped)
function localunequipped()
    laweld = la:FindFirstChild("Weld")
    laweld:Destroy()
    rs.C0 = rs.C0 *CFrame.new(-0.5,-1,0)
    ls.C0 = ls.C0 *CFrame.new(0,-5,-4.75)

end
gun.Unequipped:connect(localunequipped)