Don’t know if the ammunition pruchase is a myth or not but here are sources that I had saved;
Obama DHS Purchases 2,700 Light-Armored Tanks to Go With Their 1.6 Billion Bullet Stockpile
1.6 Billion Rounds Of Ammo For Homeland Security? It’s Time For A National Conversation
Pot, the “DHS Has 2700 Tanks” story got debunked by LGF. They only got sixteen.
Breitbart hit the “DHS Has 1.6 Billyun Rounds” story pretty hard. They only got 450 million, but for the size force they have that’s still overkill.
There is too much chaff (military-grade tinfoil) floating around the blogosphere, but the facts are buried deep inside. You just have to wade your way through.