Here's something I've turned over in my mind before and I've never seen a good discussion over. This seems like a good of a place as any to ask.
I have adapted some personal security tools and techniques in my life to reflect my status as an apartment dweller, one of which has been to sit down and draw a detailed map of my dwelling place and figure out which lanes of fire are safe and which are likely to injure an innocent bystander.
The wall between these units, although soundproof, is an illusion. Even a .22 would penetrate one of these units from end to end.
To that end I've figured out that there are exactly two directions I could fire and not violate the fourth rule of firearms safety because I know there is no good reason a person would be there, and I know there is a backstop. It's not even safe to point anything straight up as this would violate the second and fourth rule.
Fortunately it works out these are also the directions from which an invader would enter.
I further take the precaution of using JHP 110 grain .357 cartridges. I favor 125 grain loads normally, but I feel stepping it back some is necessary to insure that my backstops (steel storage buildings full of maintenance equipment with wooded lots and then dumpsters behind them) will stop a stray round.
A long gun seems to be out of the question with my current arsenal, and would be difficult to keep in a "ready to go" condition in any event. For the longest time I thought the use of a long gun for my personal protection in my abode was simply not feasible if I wished to remain safe.
Let me be upfront about this: I have made arrangements and have discretely scattered non firearms about my small space for the unlikely event someone would be in a "prohibited space", i.e. a space where I could not ethically point a muzzle.
I've been told that two layers of sheet rock should stop frangible 5.56 catridges or certain 20 gauge loads. To be honest the thought of a shotgun in this situation does not appeal to me, but a light rifle round seems feasible.
See when it's your own house, and you don't literally share walls with your neighbors, you have a lot more control over the situation and you can safely use a very effective firearm. But when you can't know where the people in the next unit over are physically located at all times, you have to plan a little more and look at using less effective tools in the interest of the safety of others. I figure as long as I use a handgun caliber, and use non-FMJ catridges that aren't loaded too hot, I am obeying the four rules.
I probably should get some Glasers, but I don't understand how I can expect them to perform to be honest. I want to stop aggressors not make them angry.
My query is, is there a long gun for this situation, be it a rifle or a shotgun? I have even considered if a carbine in a pistol caliber could be the answer.