They’re going to need a lot more ammo than 1.2 billion rounds.
Serious shooters can go through over 50,000 rounds per year just to stay in tip top practice - especially if they shoot a semi auto in 5.56. For 5.56 competition shooting 2000 rounds per month for a serious competition shooter is the norm and that's about 24,000 rounds per year
2000 or so rounds per year is the minimum each and every LEO must shoot to keep his weapons authorization current.
There’s probably 1.2billion rounds in the small county I live in.