I think that as WWIII drags on into 2000-2001-2002 etc, you would start to see more and more "primitive" weapons with maybe one or two "modern" weapons held in reserve.
The black powder gun would probably be one of the first "primitive" weapons developed. Along with the wooden bow, and maybe the cross bow for the first line of fighters, backed up with the "Brown Bess" musket, or if you have a gunsmith with real talent, you have either the "Kentucky" long rifle, or possibly the American Civil War "Springfield".
The way I look at it, if my "primitive" Brown Bess Musket keeps you from stealing my pigs, so what.
My $0.02
Mike