There are two types of gun owners in the world- those who have had an AD and those who are going to.
I’ve had an AD but never an ND. Mine was a malfunctioning Citori. When you closed the action the top barrel would fire. Not every time, but it did it twice and was repeatable without a live shell.
Only safe handling practices prevented a tragedy. I took it to a gun smith, he said he fixed it and I traded it even for an A5 at a gun show the next weekend. I never put another shell in it after it went off the 2nd time and the 2nd was done very carefully trying to repeat the first time to make sure I hadn’t done something stupid. Incredibly scary.