Jcub, first, thanks for your service.
I'm not one of them, but a lot of our members have been in fire fights and similar situations.
Next, in your scenario you state generally, that anarchy breaks out in our country. I live in Montana in a somewhat rural setting. The vast majority of the population of Montana are armed and many are well armed and have no reason or motivation to become anarchists or do what happened, say in LA or New Orleans. So the one gun anarchy scenario is difficult to picture here. But, playing along, if anarchy did break out in the rest of the country, I vision it happening in the more urban areas and possibly spilling out with looters and such straying out to the rural areas.
Now, you are more experienced with guerrilla fighters vs anarchists and you were a foreigner in a foreign country in Afghanistan which is a much different secnerio. I am a Montanan in Montana and any anarchists that I might encounter would likely be strays form urban areas and would have a very short life expectancy in this part of the country. Hence my choice of weapon, a bolt gun in 223. Very effective on humans and game. The only reason I picked a 223 vs say a 300 WSM is logistics. A 308 would have been another good choice. Large amounts of 223 ammo are much cheaper and easier to deal with than larger cartridges. If I were a shop owner in LA, or otherwise an urban dweller, I would choose an AR, AK or SKS type of weapon.
The most likely form or scenario of unrest to possibly happen in this country would result from an over reaching government imposing more restrictions and attempting to disarm the citizenry. The sheriffs in Utah wrote a letter to the president on that subject. Not exactly an anarchy scenario.
So although fun to play along, nation wide anarchy means differnet things in different areas, and is not likely to happen. The one gun scenario will never happen. But if it did, I'll take a 223 bolt action.