Indeed.
If there is TOTAL societal and economic collapse there will be no way for the government to control the populace whether they have 1.6 billion bullets or 1.6 trillion.
At the point of collapse the monetary income to the government would effective drop to zero dollars as no one will be paying taxes. How long do they think they can retain command/control of an army when they are no longer paying them or are able to supply them with basic needs?
As they attempt to transfer ammo (or food or whatever) their supply lines will be decimated as the only law of the land will be survival.
If they are buying ammo to try to manage a total societal break down, they are playing a fools game.
They could use excess ammo stores as trade goods to manipulate/ coerce power blocks outside of their organization.