[NWPilgrim]

It seems common sense that any ammo capable of RELIABLY penetrating enough into a perpetrator, perhaps heavily clothed, is also capable of penetration inch or more of drywall. Some ammo is designed to be frangible, but I question if they only penetrate sufficiently under ideal conditions and are at risk of failing to under less than ideal conditions.

I agree you should get to know the construction of all your condo walls, floors and ceiling. Then consider the most likely directions of shooting in possible threat scenarios. Probably not many directions to worry about: someone busting through front door, shooting from your bedroom into hallway, etc. Then see if any of those directions can be made safer with reinforcements such as heavy bookshelves, metal wall decoration, etc. The reinforcements may not prevent total penetration but could some reduction in velocity and range past your walls.

On the other hand, you don't want a cartridge or ammo known for over penetration such as FMJ, heavy loaded magnums, etc. Hollowpoints often plug up when encountering barriers such as drywall and act like FMJ anyway. But a soft lead tip HP might deform more on barriers yet still penetrate clothing and flesh enough. Perhaps a .38 Special loaded with lead hollowpoints? In fact, one of my nightstand guns is a .38 S&W loaded with Federal Nyclad 125 gr. ammo. Nyclad is a soft lead bullet clad in thin nylon jacket/coating.

In the end, you have to weigh the risk of NOT defending yourself effectively against the risk of injury to others through unintentional misses. And take what precautions you can through planning and preparation of the condo and your reactions. You can reduce the risks of over penetration, but not eliminate the risk totally if you use a reasonably effective cartridge.