Yes they have. It is well documented by the GAO office itself stating that it is investigating due to the HUGE ammo purchases. I haven't the foggiest idea why you would say otherwise when it is a matter of public record. Can you elaborate why you think that the GAO is lying?
Give me a link to that GAO report, please... as all I have seen is an authorization for the Department of Homeland Security to purchase "up to" 1.6 billion rounds total of all calibers over the next 5 years.
This contract covers ammo for Customs and Border Protection, Citizenship and Immigration Services, the Federal Emergency Management Agency (FEMA), Immigration and Customs Enforcement, the U.S. Secret Service, Transportation Security Administration, the DHS police force, and all the guards that protect the various buildings these agencies are housed in.
This is an authorization, not an actual buy... and a simple calculation of the number of rounds actually expended per Federal agent (of all the above agencies) per year in training accounts for nearly all of that ammo. They are required to qualify 4 times per year, and each qualification uses ~150 rounds including required practice sessions. This totals 600 rounds per year per agent, while each agent's share of the "1.6 billion over 5 years" is ~800 rounds per year. DHS by itself has between 65,000 and 79,000 armed agents.
Specifically, under that authorization DHS has contracted with manufacturers for a "guaranteed supply of up to 450 million rounds of .40S&W hollow-point ammo over the 5 years"... the rest is for 9mm and other calibers used by DHS and the other agencies.
In April this year Congress held a hearing, and much was made about the ammo contract providing more ammo for training of Federal agents than the Army uses for its soldiers... but the reality is that the Army (and Marines, etc) have gone to extensive use of "bullet simulating technology" for a lot of training (specifically to cut ammo costs). The Army numbers also include the majority of Army personnel who have non-combat jobs, and who thus qualify once per year (and do no other live-ammo training). So with Federal agents qualifying 4 times as often than most Army personnel, its not surprising that they would use more.