Earlier quoted context omitted.
Well, among the key facts necessary to understand that is that the "safety features" are not pure cost-free benefit, and the NRA believes the costs outweigh the benefits. They have some decent arguments for the existence of the costs; reasonable people could disagree about the relative degree of each. It is also not generally the case that guns are always "bad"; guns are also significantly used in self-defense, usual…
http://www.juancole.com/2012/07/58-murders-a-year-by-firearm...
Therefore, the only conclusion available is that the theory is incorrect.
You may be able to salvage pieces of the result your are trying to obtain by a more careful analysis, but the facts do not permit "guns = gun crime" to be sustained at such a simplistic level. By the time one is done examining what the facts do sustain the result is far, far weaker.