Its kinda weird but for the money involved my suggestion for people is a .44 Magnum revolver, with a long barrel on it (8″). And get it fitted for speed strips if it isnt already, and get a bunch of the strips for it. It makes a revolver about as fast to reload as a semi-auto.
This replaces the shotgun, its a one-shot-stop and it does significant damage to doors. You can shoot it from the hip at knife-drawing range and it doesnt matter where you hit someone with it (arm or leg, and that appendage is coming off).
A Taurus revolver is about $650, or half the price of a desert eagle. You dont gotta worry about the ammo being rare if you’ve got 500+ rounds stocked up. And by the time it eventually does run out, you will at least have had multiple opportunities to get a replacement.
Serves the role of a glock too, and it does it better. Unless you’ve got 17 zombies to worry about I dont think 6 shots is going to put you at a disadvantage, especially if you’ve got the speed strips.
In shtf, if you find ammunition you are most likely going to find the gun that shoots it, laying next to it. Otherwise youll find alot more weapons that dont have ammunition for them, which also fire common calibers.
Prepper gun choice should be about choosing a weapon that will be effective and will carry you through the initial phase of it.
If you Are concerned about ammo availability, then you should pick a caliber that is Not Common but still commonly carried in stores. Sounds like an oxymoron doesnt it? Well a .357 magnum is less popular but you can usually still find it, and you can probably find some 30-30 too (there are low cost lever actions that can hold up to 7 rounds).
Most combat in shtf is close range, home invasion style, or shooting across a parking lot. And if they have a rifle then you should just find cover and avoid them. You dont need to shoot farther than 100 yards at most. And even a 9 mil will shoot reliably up to 100yd with a scope (estimated effective range of a 9mm round is 150 yards, anything lower is user error).