How do I make mags in this gun script?

I am make a gun and everything is perfectly fine but i need to make mags in this script and I don't know how. Here is the script:

Player = game.Players.LocalPlayer
Gun = script.Parent
Ammo = 20
MaxAmmo = 20
mouse = Player:GetMouse()
BulletDamage = 10
enabled = true
function Shoot()
    if Ammo >= 1 and enabled == true then
        enabled = false
        IsFiring = true
        Firing()
    end
end

function Firing()
    repeat wait(0.3)

        function Damage(Part)
            if Part.Parent:FindFirstChild("Humanoid") ~= nil and Part.Parent.Name ~= Player.Name then
                Part.Parent.Humanoid.Health = Part.Parent.Humanoid.Health -BulletDamage
                Bullet:Destroy()
            end
        end
        Ammo = Ammo -1
        print("You have "..Ammo.." ammo left!") 
        enabled = false
        Bullet = Instance.new("Part", Workspace)
        Gun.GripPos = Vector3.new(0,0.3,0)
        game.Debris:AddItem(Bullet,2)
        Bullet.Shape = "Ball"
        Bullet.Size = Vector3.new(0.1,0.1,0.1)
        Bullet.TopSurface = "Smooth"
        Bullet.BottomSurface = "Smooth"
        Bullet.BrickColor = BrickColor.new("Really black")
        Bullet.CanCollide = false
        Bullet.CFrame = Gun.Handle.CFrame
        Bullet.CFrame = CFrame.new(Bullet.Position,mouse.Hit.p)
        BM = Instance.new("SpecialMesh",Bullet)
        BM.MeshType = "Sphere"
        BM.Scale = Vector3.new(0.2,0.2,0.2)
        v = Instance.new("BodyVelocity", Bullet)
        v.velocity = Bullet.CFrame.lookVector *90
        v.maxForce = Vector3.new(math.huge,math.huge,math.huge)
        Fire = Instance.new("Sound", Bullet)
        Fire.SoundId = "http://www.roblox.com/asset/?id=131419157"
        RP = math.random(10,20)
        RP = RP/10
        Fire.Pitch = RP
        RV = math.random(70,90)
        RV = RV/10
        Fire.Volume = RV
        Fire:Play()
        game.Debris:AddItem(Fire, 2)
        Bullet.Touched:connect(Damage)
        wait()
        Gun.GripPos = Vector3.new(0,0,0)
        enabled = true

    until IsFiring == false or Ammo == 0
end
function StopShooting()
    IsFiring = false
end

function Reload(key)
    key = key:lower()
    if enabled == true and Ammo < 20 and key == "r"  then
        enabled = false
        RS = Player.Character.Torso["Right Shoulder"]
        for i = 1,4 do
            RS.C0 = RS.C0 *CFrame.Angles(0,0,0.2)
            wait()
        end

        repeat wait(0.1)
            Ammo = Ammo +1
            RS.C0 = RS.C0 *CFrame.Angles(0.2,0,0)
            Shell = Instance.new("Part",Workspace)
            Shell.TopSurface = "Smooth"
            Shell.BottomSurface = "Smooth"
            Shell.Reflectance = 0.01
            Shell.BrickColor =BrickColor.new "Black"
            Shell.CanCollide = false
            Shell.Size = Vector3.new(1, 1, 1)
            ShellMesh = Instance.new("BlockMesh",Shell)
            ShellMesh.Scale = Vector3.new(0.2,0.3,0.45)
            game.Debris:AddItem(Shell,0.8)
            Shell.CFrame = Gun.Handle.CFrame *CFrame.new(0,-0.5,-0.3)
            wait(0.1)
            RS.C0 = RS.C0 *CFrame.Angles(-0.2,0,0)      
        until Ammo == MaxAmmo
        for i = 1,4 do
            RS.C0 = RS.C0 *CFrame.Angles(0,0,-0.2)
            wait()
        end
        wait()
        enabled = true
    end
end

mouse.KeyDown:connect(Reload)
Gun.Deactivated:connect(StopShooting)
Gun.Activated:connect(Shoot)

Please help THANKS!