Have you considered getting a silencer that you could use with a quality .45 ACP handgun? That would give you a reasonable defensive cartridge, sub-sonic projectile and protect your hearing.
You might want to read some posts in the NFA Guns and Gear section of this forum.
NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor
"When plunder becomes a way of life for a group of men living together in society,
they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat