Why is DHS stockpiling so much ammo?

Hot Air reports:

Even realizing that he was going to immediately be labeled as a Right wing conspiracy theorist by the Left, Congressman Jason Chaffetz posed a rather pesky question to the Department of Homeland Security this week which is sure to get a lot of tongues wagging. Why do they need to purchase huge stockpiles of ammunition? Far more, in fact, than the the Army buys on a per capita basis.