Guns don't kill people, bullets do. We should classify them as a controlled substance, placing the sale and distribution of bullets under Federal oversight. As a controlled substance, the government could levy punitive taxes on the sale of bullets, thereby making mass arsenals a prohibitively expensive proposition.
As with any controlled substance, the government could apply safety regulations and require agency approval before any new product is introduced into the market – much as we do with food and drugs today. This would allow some bullets, such as those used for hunting or small caliber weapons, to be considered acceptable while others, such as hollow point or “cop killer” bullets, to be banned outright.