I have been giving this a great deal of thought. Watch some of these doomer movies like "Book of Eli". Guys are pulling semi-auto .45's and nines, RPG's and machine guns and blazing away like there's no tomorrow. The movie takes place 30 years in the future. There's a real good chance the propellant on that RPB won't function and the explosive will be so unstable pulling the trigger will cause the whole thing to fizzle or blow up in the operator's face.
Same with semi autos and machine guns. The springs in the magazines and the firing pins would be the first to go out. Most semis have a maximum amount of ammo that can go through them before they have to have barrel replaced. The more rounds fired, the sooner that expiration date comes. And in a violent world, it's not going to last 30 years.
That's why I have been giving a great deal of thought to stockpiling the most simple firearms available. Things like single action shotguns, revolvers and bolt action rifles. 10 or 20 years from now, the only functioning weapons will be the ones with the fewest number of moving parts. Open the breech, put in a round, close breech, cock, aim, fire.
The slower rate of fire means the barrel and other parts will last longer. That includes the fasteners holding the barrel or trigger assembly to the stock or grip. I was once at the range where someone was using an original Thompson from WWII. With every magazine, he had to check every fastener as they had a habit of coming loose. Imagine the result if the stock slipped off the assembly while firing.
A bolt action 30.06 basically can fire even if the magazine spring is missing; just load one round at a time and fire. It's slow, but 20 years after, your attackers may be armed with wooden bows, spears and rocks. Who has the technological advantage then?
A single action revolver has one moving part - the trigger and hammer assembly. I guess if you slammed the hammer side down on a rock you could make the gun useless, but not much more would do it (Edit - the spring in the extractor might go out over time).
I think if I had to move up the food chain, a level action or slide action weapon may last a while, but sooner or later the springs would go out there as well.
Here's the other kicker: Cost. I was in a pawn shop recently and a buyer picked up a single action 12 guage shotgun, no name, for $85.00. That gun will literally last 100 years and can be left in the trunk for just in case. You could buy a dozen guns like that for the price of a single, stripped down M1A and still have some money left over for ammo.
I don't know about you, but guns like this are on my list for having on hand long after the AR is unusable and the .45 auto is nothing more than a fancy hammer.
Mountain House Freeze-Dried Food