It wouldn't take an act of Congress to make ammo hard to find.
All the EPA would need to do is say that the lead in it is a hazard, or the primer/powder causes cancer. They could drive prices up astronomically for the presumed cost of clean up of using lead cartridges on public land.
Taking guns away would be harder, but it wouldn't take much to reclassify what is an "appropriate" handgun and rifle for a citizen to own, based on size, ammo capacity, barrel length, etc. They can use the recent shootings as an example, as they've been trying already to outlaw "extended mags." The media already thinks that 15 rounds in a 9mm is "extended" even if it's the stock mag that fits flush with the grip base.
Or they could do Euro-style and say you can't own any gun that uses a military and/or Police cartridge.
If you talk to many hardcore liberals, they really think that an enlightened society has no need for lawful gun ownership. And if you want to run the 2nd amendment through the mindset of creative left-leaning judges, all you may be entitled to is a single action breech-bolt operated rifle locked away in a government approved safe... after you have applied for all the necessary tax stamps, government approved training courses, been placed on a national registry of gun owners...
It's possible.
Not likely, but at least half of the population thinks we need more gun control.