There is a pretty simple answer to that question.
An” End of the World Gun” is a firearm that is so simple & basic by design, so reliable & durable, so easy to use, that it could survive the “End of the World”.
Chances are that as a gun owner you probably already have at least one such firearm sitting in a closet or safe. Probably something that you rarely take to the range and probably don’t think about too much.
The reason you don’t think about them too much is because most “End of the World Guns” are older, more basic designed style firearms, things so antiquated by today’s standards that they are inherently simple and reliable by design.
Some features you’ll want to look for in an “End of the World Gun” are non-semiauto, bolt action, break action, single shot and even lever or pump action and lever action.
Some great examples of “End of the World Guns” are, Mosin Nagant, or any good solid bolt action rifle, single or double barrel, break action shotguns, most of your standard double and single action revolvers, Rossi or H&R break action single shot rifles, Marlin lever action rifles and any pump action shotgun.
So there you have it. You’ve probably got one or two “End of the World Guns” already in your collection and even if you don’t most of ’em are pretty cheap to pick up.