A LocalScript in a tool in startergui
script.Parent.Equipped:connect(function()
    local event = game.ServerStorage:WaitForChild("Events").Gun.AmmoGui.AmmoOpen
    event:FireServer()
    print("Sent!")
end)

script.Parent.Unequipped:connect(function()
    local event = game.ServerStorage:WaitForChild("Events").Gun.AmmoGui.AmmoOpen
    event:FireServer()
    print("Sent!")
end)

script.Parent.Activated:connect(function()
    local event = game.ServerStorage:WaitForChild("Events").Gun.Main.Shoot
    event:FireServer()
    print("Sent!")
end)

The server script in replicatedstorage

local e = game.ServerStorage:WaitForChild("Events").Gun.Main.Shoot
e.OnServerEvent:connect(function(plr)
    print("Recieved!")
    local Gun = plr.Backpack.Gun
    local mouse = plr:GetMouse()
    local Ammo = Gun.Ammo
    local bullet = Instance.new("Part",game.workspace)
    bullet.Shape = "Ball"
    bullet.Size = Vector3.new(0.5,0.5,0.5)
    bullet.TopSurface = "Smooth"
    bullet.BottomSurface = "Smooth"
    bullet.BrickColor = BrickColor.new("Really Black")
    bullet.CanCollide = false
    bullet.Anchored = false
    bullet.Name = "Bullet"
    --CFrame Stuff
    bullet.CFrame = Gun.Handle.CFrame
    bullet.CFrame = CFrame.new(bullet.Position,mouse.Hit.p)
    --body velocity
    local v = Instance.new("BodyVelocity",bullet)
    v.velocity = bullet.CFrame.lookVector * 90
    v.MaxForce = Vector3.new(math.huge,math.huge,math.huge)
    game.Debris:AddItem(bullet, 5)
    Ammo.Value = Ammo.Value - 1
    if Ammo.Value <= 0 then
        repeat
            Ammo.Value = Ammo.Value + 1
            wait(0.3)
        until Ammo.Value == 40
    end
end)