For amendments desired by congress, a 2/3 vote of BOTH houses is required to PROPOSE the amendment -- but said amendment is not valid and is not part of the United States Constitution until it is ratified by 3/4 of the states. (And who here thinks there is any real chance of THAT happening with an amendment that guts the original 2nd?)
Even if Obama manages to get a "gun banning treaty" ratified in the U.S. senate it will be null and void as far as our gun rights go. His administration cannot legally impose any UN gun ban in the People of the United States.
That's not to say he and his proposed "civilian national security force" would not some day try to do it illegally, but I think THAT really would provoke a 2nd American Revolution.
Treaty it is not an Amendment. Treaty need only be ratified by the Senate. The House has nothing to do with Treaties.