Here's a good short on why birdshot is best for home defense in an urban area such as an apartment Birdshot is better unless you really fucking hate your neighbors that much.
Also Which birdshot are we talking about 8 birdshot which is very tiny pellets or 4 birdshot.
Not all birdshot is the same. Number 8 birdshot is used for quail and duck hunting. Number 4 birdshot is used for turkey and even taking care of varmint sized game at times.
Just saying here People acting like you need 12 gauge buckshot for self defense only don't understand getting shot isn't fun. There is also no shame in using a smaller caliber that you can control.
Also can people stop treating Birdshot like its rocksalt if you get shot with rocksalt your going to have a nasty sting and its going to hurt. You get shot with birdshot you're not going to have a good time and probably need an ER trip ASAP.