As suggested, the claim that the NRA is the lobbying arm of the ‘big’* gun manufacturers is nonsense. The NRA is the lobbying arm of millions of gun owners (though by no means does it represent all gun owners). Love or hate the NRA as you like, that’s the reality.
*the pure gun manufacturers are all much too small to be in the S&P 500; Olin is similar in size to companies right at the bottom of the S&P 500 but isn’t a component, or a pure gun manufacturer (owns Winchester among mainly unrelated businesses). Some actually large companies are involved in gun retailing, eg. Walmart, but it isn’t a big part of their business.
I think the rightists and especially the far rightists have larger arsenals per capita than do the middle & left. But there’s still a hefty supply of lefties with more guns than they can shoot at once.