You know, I just had a funny thought.

Technically speaking, certain obsolete firearms should be plenty adequate for a "home defense" type application, but useless for a mass shooting.

A double-barrel or triple-barrel flintlock blunderbuss comes to mind - capable of two or three very loud, very smoky, very powerful shots before needing a long and involved reload.

And for "doomsday prepper" types - it's fairly simple to make black powder & paper cartridges from scratch compared to modern ammo.