That’s 2,250 rounds _each_.
And most of ‘em won’t be getting _any_.
DHS has three weapons training facilities, each of which expend about 20m rounds a year. The Federal Marshals service and the FBI have their own weapons training facilities. So just as a guesstimate, you are looking at around 100m rounds for training every year.
Based on the downright enormous training ammo consumption seen every year in the US military, a contract of just 450m rounds does not come across as that outrageous.