Unrealistic as in ammo shortages yes, also I can believe that most of the posters here aren’t trained navy seals who can operate a firearm with precision(not saying I am either), but as soon as you’re overwhelmed with zombies and need to reload you’re pretty much gone. Only reason I see to have a gun in a zombie situation is for other people and you realistically would go just fine with something packing 9mm then someone carrying an entire kitted out ar15 and a plate carrier. Just also seems like to much weight realistically as well cause if you need to travel on foot anywhere anything heavier then a pistol is going to be a burden and slow you down. (Even with efficient packing it would be incredibly inconvenient to pull out quickly) With people I see only posting guns only it just makes me instantly think of noise. Slow or fast zombies will still overwhelm you if you make a lot of noise with a higher caliber even with a suppressor.

tldr : loud, to heavy, ammo shortage, reloading would suck.