The point about local gun ownership and the number of relics that American's keep is huge. At this point I think we are at 1 Gun per 1 person in the country, which is as high as anyplace in the world. I don't think I would feel safe without one.
I also think Ammunition would be the primary driver of which weapons were still used and which became hat-stands and blunt weapons. Even if continually manufactured, there would be a limited variety of ammo produced - and only weapons that fire that ammo would still be viable. There would be some conversion I'm sure as well, but the fact that older weapons can still fire Some of the modern Ammos will keep them in use long after the apocolypse.
Lastly, the newer guns are going to be the most popular right after the war, and they will clearly get run-down, worn-out and eventually discarded. 200+ years after the war, the less-popular guns initially will be the ones that are still in good shape, and viable as weapons. The rugged-nature of the older weapons will also add to their longevity.
I really liked the old-weapons in Fo3, like the level-action rifle - sends me right back to frontier times. All that was missing was a coon-skinned hat!
