You are all fools. None of what you claim to be worried about will ever happen (i.e. the breakdown of society) but IF IT DID who do you think scoffs at you stockpiling small caliber firearms?
The people who would have the power in the aforementioned (quite impossible) situation are the Military.
If you really want to run around raping and pillaging a post apocalyptic wasteland, your best bet is to join the USMC, US army, or Air force. The rest of you are pissing on a forest fire.
Hate to break it to you but I will tell you first hand that ALL the vehicles, missiles, guns, ammunition, etc used by the US military that you feel give them the upper hand over our puny small arms? Yeah they are all engineered, produced, programmed, assembled and sold to the government by private CIVILIAN CONTRACTORS. That supply chain would break down VERY quickly and create a logistics nightmare that would stop even the US military dead in it's tracks without missiles, fuel, etc.
The military would NOT have a monopoly on said gear for long in a true SHTF situation. A couple government shipments sabotaged by the engineers producing them, a couple Javelins get out to some civilian groups, some convoys or outposts get taken, etc. The playing field would be leveled VERY quickly.
Also grenades, missiles, explosives, eg: heavy military ordinance, is NOT hard to produce or procure, there just isn't a civilian market for it because it's not legal in peace time. In SHTF, nobody will care, those things will be mass produced or stolen and proliferated on the open market by the thousands of people who produce them now for government and agricultural use.
Machine guns aren't hard. In a world where the ATF and FPMITAP is non existant, with access to a *minimum* a dremel and some scrap metal, all my rifles are full auto in less than 24 hours.
And that's assuming the just as unlikely scenario that the entire CIVILIAN VOLUNTEER US military force sides against the civilian population. eg: the very same soldiers that see first hand how important civilian gun rights, etc are in Iraq, etc.
Thanks for playing.