Based on the advertisements for their sale, I'd like to suggest that a cost-effective way to cut down on the proliferation of Big Guns (and incidentally probably reduce the ownership of oversize SUVs) would be for the government to subsidize the pharmaceutical industry to provide any man who wants it lots of free Viagra®.
(Go read my comment to daveon's post before you suggest I'm some sort of gun-hating communist socialist anti-American. I own a rifle/shotgun and have used it. I do not advocate the wholesale confiscation of firearms. I simply have no patience with Gun Nuts.)
Update: Link to the advertisement in question included due to comment asking for clarification.