Just to point out, the "mass purchase by DHS" is not really anything such.
DHS consolidated the request for bid for all the component agencies. So instead of CBD having a contract, and ICE having another contract, and Secret Service having another contract, and FLETC having another, etc, etc, they actually did something smart and put out one big request for all the ammunition.
And then, some people saw the RFB and did not know how to read it. Each line item (caliber and type of ammo), has a quantity and a delivery/billing per order amount.
So they might request a bid for 100,000 rounds of ammunition in 1,000 round batches. The maximum buy is 100,000 rounds, but a component can order in 1,000 round increments.
The people who started this rumor multiplied the total quantity and the batch size, and reported that they had ORDERED 100,000,000 rounds. A) The maximum amount was actually 100,000 rounds, and B) this was NOT an order, it was a RFB, that means they may order up to 100,000 based on need. They could order NONE, or all 100,000 rounds. And no more, without renegotiating the contract.