They don't generally have firewalls between individual units
Good point. At the amount if upgrades the OP would need to do its much better to moveLife is only as hard as we make it. If your neighborhood and town are so bad that this is what you seem to be so concerned about, the only thing that I see as a probable fix for your question is find somewhere else to live. If you are worried about shooting innocents and maybe even your children, then the fix is move. Yes, I know you said at the start of your post that this was not an option. Why not? Are you chained inside your apartment? Maybe it's time to stop watching video scenarios of actions that will probably never happen to you, or if you are so concerned that they will, then move.
Ralph
A "firewall" is multiple layers of sheetrock thick enough to stop a fire for a set amount of time.Drywall itself is an excellent firewall.
I can see your knowledge of residential construction is equal to your knowledge of firearms and huntingModern building? Built in the last 20ish years? Only interior walls are dry wall. You're living in a big, concrete, hollow, brick. Other than the door, buck shot will just bounce. Very likely hitting you or yours.