Whatever guns you have for a SHTF scenerio they are going to be for only a couple things:
1. Protecting what you got from other people intent on taking what you got. Probably small groups or individuals
2. Used for taking game to provide food on the table.

This is just my opinion, but the illusion of fighting off hundreds of people and needing thousands upon thousands of rounds is imo just ridiculous. The reality is, if you face even a small group, say squad size, of an organized, trained and equipped force- you are toast. What do you have to fend off supresive fire from LMG's, grenade attacks, and heaven forbid artilary or airstrikes.
It is just a pipe dream. What you need is a safe place to hide out.
Just trying to survive in a non functional society will be hard enough, let alone with people out there trying to kill you.

Hemi