Couple points here.
Until the citizens of the US stand up and fight for our right (to party, among other things), We will continue to suffer the threat of gun control and restriction. There are a few issues with the UN Small Arms Treaty, both legal and societal.
1) The supreme court ruled in 1957, Reid vs. Covert, that The Constitution of the United States supercedes any international treaties. This isn't to say that this and other treaties aren't going to affect our accessibility to guns and ammo, but not to the far reaching effects the UN hopes for.
2) In the possibility of confiscation, who would you suggest do the confiscating? If this issue ever got to the point, we'd quickly cross into the realm of revolution. One of the main reasons is a large split in the members of our Armed Forces. A good chunk of them, if not a majority, will refuse to participate in an arms collection. How would the confiscation be performed? Turn in points? I can assure you that none of my weapons would be found there. And I sincerely doubt that I'm in the minority of gun owners that would take that stance. Door to door search and seizure? Lets trample on the constitution some more, not to mention the issue of the manpower capable of doing such a search, as well as the odds of any weapons actually being there. Hard to keep something on that large of a scale secret. Plenty of warning for those of us who would stash our guns, or just disappear ourselves.
3)Per the small arms survey in 2007, the US citizenry owns a little over 1/4 of the worlds guns. That is around 270 million. Thats a lot of guns to confiscate, petty much impossible. The higher likelihood, which many people have already touched on, is an increased attack on ammunition,ability to use the firearms, and firearm accessories. An AR doesn't do much good if you can't buy the magazines for it. Its tough to reload your own ammo if you can't obtain the materials, or can only obtain them in small amounts at one time. If you can't go anywhere to shoot your firearms, your skills diminish, and you become less of a threat (because we are viewed as a threat).
There are several different methods of ammunition stamping being studied, researched, and even implemented in the small scale even now. All will increase ammo costs significantly, and the results are mediocre at best. I fully believe we'll see limits on the amount we can purchase at one time, the quality, and the type.
