They can't ban guns but they can make ammo a lot harder to get. The Obama motto is, "If you can't legislate, regulate instead". The 2nd amendment does not mention ammunition or projectiles in any way. Also, due to "environmental" contraints during the manufacturing process and the increased power of the EPA, ammo has already more than doubled in price since Obama took office. In addition, the EPA is also looking at the environmental impact of spent lead ammunition.
It has already been suggested by some lawmakers to require ammunition manufacturers to put an electronic chip in every bullet that would need to be registered to the owner. The costs involved in implementing and regulating this would virtually eliminate recreational shooting by anyone but law enforcement...or rich people.