Briefly, they claim they have 263 million rounds in inventory, they use 88 million rounds a year for training, and buy 105'ish million a year.
Interesting numbers... but nowhere near 1.6 billion rounds.
Though the numbers do seem to indicate they are building up their inventory by 18 million rounds a year? And why do they need 3 years worth of ammo stored in inventory?
That's a flat ass lie they wouldn't use that many rounds if they were in the middle of a civil war.