Presumably the money which is wielded by the gun lobby comes from people who spend a lot on guns. The gun firms then proceed to spend a fraction of the profit they make from gun sales on finncing lobbying against gun laws. Since there are more people who don't spend a lot of guns, that means that in principle there should be a lot more money available to outspend the gun lobby.

Presumably the people who see preventing sensible gun laws as their priority (I mean the kind of things that gnu favours) must be a great deal more dedicated to their cause than the ones who see preventing school massacres as a higher priority.