The proposed UN "treaty" deals mostly with small arms sales among countries, not within them. Ever since WWII, the US and the Soviet Union have been selling "arms" to just about any country with cash and in some cases even those with no cash. Why do you think there are so many AK-47's around the world. There are those who think that all these conflicts in the world can be eliminated if the arms trade was curtailed. Wrong thinking as first they have to fix the reason these people are fighting. Countries have been created and divided according to the convenience of other world powers. Iraq was created by the British out of three separate ethnic areas. Syria, Saudi Arabia, Jordan, and even Israel are all products of either the League of Nations, the UN, or the British while they administered areas under mandate. Look at all the good things that have grown out of this mismanagement.
As for the UN having effect on Guns in this Country, there's something standing in their way. Our Constitution and the 2nd Amendment.
Remember that most of those who are screaming the loudest over this UN proposal have a financial interest in the form of raising money. The bigger the scare, the more money they can raise. The NRA is just as bad as all the other groups in fanning the flames.
For myself, I have a simple plan for those who come for my guns. I will willingly give them up, piece by piece with the bullets being first.