Well you have to ask how many armed agents work under the DHS. They have 7 sub agencies the customs and border protection, Immigration services, U.S. coast guard, FEMA, Secret Service, TSA, Federal law Enforcement Training Center.
Then you have to figure how many rounds does each agent need to practice and stay qualified each quarter ? Also how many replacement agents will they need each year and how many rounds will it take to get them proficient to be qualified ? Most of the contracts for all that ammo are filled over a 3 to 5 year period. Most agents will have to be trained and qualified on more then one type of weapon. 99.9% of the ammo they buy will be fired in practice and qualifying.
So when you look at it that way is that really a lot of ammo ?
I'll bet there are more DHS armed agents then the Army has in Afghanistan.
There are supposedly 200,000 people employed in DHS. I would highly doubt that even half of them practice on a regular basis. For practice, you use cheap ammunition. Not expensive hollow points which they contracted 750,000,000 over 5 years. Even with the figures of 1 billion rounds. That works out to 5,000 per employee. No agency practices that much, not even military.