Doesn't have to. "Arms" does not have a complicated definition. "The right of the people to keep and bear SOME arms" is not what 2A says.
... neither is "The right of the people to keep and bear ALL arms."
Don't get me wrong, I'm all for arms ownership. I do think there is a line, though, that is reasonable. I don't support personal ownership of nuclear missiles, land mines or RPG's, but I guess you could call those munitions vs. arms. In fact, as a country, we actively pursue those seeking to arm themselves with nuclear weapons or to use chemical weapons but refuse to intervene when the same number of people are being killed with traditional arms, so we've already established a de facto line in terms of national intervention.
I don't, however, think the "why would you need that for hunting" approach is the right one, as that clearly wasn't the intent of the Second Amendment - it wasn't about keeping Bambi from repressing us, it was about keeping the government from repressing us.
My point is it's not an easy discussion, especially with the other side defaulting to inflammatory rhetoric and emotional response.