I submit the Beretta 1201 semi-auto 12 ga shotgun. They are out of production and expensive if you can find one, but if I had to deal with a cqzc situation (say, a hallway or flight of stairs) this is the baby I'd want with me. I owned one years ago before it was stolen (and yes I AM searching for it, have the paperwork and numbers still), and as a semi-auto capable of handling up to 3 inch mag slugs, capacity 6+1, it is highly desirable in an undead breakout. The range is limited as all shotguns are (far less range with a slug but at close quarters, yes, you CAN punch through a few zombie melons if they line up!), the 1201 civilian is a smooth bore, no rifling. Firing slugs is iffy at range. I saw the effects clearly at an outdoor mountain shooting range, and one is essentially lobbing rounds downrange, barrel tilted up, adjusted for wind, they move slow enough to hear a TICK as the slug hit the target backing after firing.
Using 00 or birdshot it is a close quarters monster. There is a video of one on You Tube, some redneck firing it with not that much grace nor talent, but he does finally fire off a string, so if you find it you will see just how fast it is. They will eat ammo quickly so have plenty on hand. Not that I need to tell this to any Zombie Hunters. Ammo is your friend. A pal asked why I had SO MUCH ammo, so I took him out with me to fire the 1201. He went through a box of shells in no time. 7 rounds as fast as your finger can pull the trigger. Add that mental image to a group of Zombie Squad members in a corridor, a couple with carbines for range and a 1201 for those pesky ones who manage to get closer during reloads. SCore : Still-Humans, 25, Zombies, splattered.
If you fire slugs, wear hearing protection. It roars.And kicks as it is a polycarbon body. Very good for all weather, low maintenance. Even comes with fixed Tritium sights as on the Berreta pistol line. I'm not a techy, so sadly you will have to peruse the internet on your ownsome to get the images.