I had a roommate four years ago that had an accidental discharge in our apartment. The gun was a Sig P250 he got the day before, he spent a lot of time dry firing the pistol because of the DAO trigger. We went to the range the day after he got the gun and he fired 100 rounds and we headed home. After we got home he had a few drinks and I was helping my ex move out what she had left at my apartment, I walked outside to bring something to her car and when I got back to the apartment he wasn't there but there was the odor of burnt gun powder(I smell so much burnt powder it didn't register right away what that meant) but a minute later he walked back in and looked like he had just seen a ghost.
Right after me and the ex walked out for a minute he went to dry fire the gun some more and the liquor getting to him didn't check the chamber first. It was his first .40 S&W so he was shooting my defensive reloads that I tend to load hot. He sent a 180gr XTP through five layers of sheet rock and some insulation between apartments, through a large plastic bin of mine and my bed comforter, it then went into the neighbors bathroom through the whole lower section of their fiber glass shower/tub and the bullet rested on their bathroom floor.
Thank heavens the neighbors weren't at their apartment, that's why my roommate wasn't in the apartment when I stepped back in, he was banging on their door.
Police showed up and were totally flabbergasted by the bullets penetration, they asked where the he!! the ammo came from.
The police did arrest him, saying he intentionally pulled the trigger so he intentionally fired the gun in a residential area, but he got off pretty clean after court.
During this whole thing NONE of my neighbors heard the gunshot. I had a lot of explaining the next morning why the cops showed up and arrested my roommate, they couldn't believe they heard nothing.
Ended up being a positive turning point in my life because from that point on my only goal was to buy my own house and that incident was a huge driving factor. Now that I know my apartment neighbors couldn't hear a gunshot in the same building, I could set a gun range up in my basement and my new neighbors would have no idea!