Reload isn't correct (nearly correct, just an error)? [Mistake]

Mouse.KeyDown:connect(function(key)
    key:lower()
    if key == 'r' then
        if IsFiring == false and Ammo.Value < MaxAmmo.Value and StoredAmmo.Value > 0 then
            AmmoNeeded = MaxAmmo.Value - Ammo.Value
            if StoredAmmo.Value >= AmmoNeeded then
                Ammo.Value = Ammo.Value + AmmoNeeded
                StoredAmmo.Value = StoredAmmo.Value - AmmoNeeded
            elseif StoredAmmo.Value < AmmoNeeded and StoredAmmo.Value > 0 and IsFiring == false then
                AmmoAvailable = StoredAmmo.Value - Ammo.Value
                Ammo.Value = Ammo.Value + AmmoAvailable
                StoredAmmo.Value = StoredAmmo.Value - AmmoAvailable
            elseif StoredAmmo.Value == 0 then
                print('Out of Ammo!')
            end
        end 
    end
end)

it does Reload, but I noticed that I had 17 Ammo, so I pressed 'r' and then it changed to 7 and then I check storedammo, so they ere like balancing, one of the turns 17 the other turns 7 and the the other ay after I press 'r' again... also, this Script, is fully Made by me, and the Proof is that the Script above is bad, and I alays do stuff badly :(