Second this. Unless you're sawing the barrel to a third, it doesn't actually work how youd think if you never used a real shotgun.

In reality the best things about shotguns in self defence are that if you miss, you probably dont kill your neighbor. The bad part is there is very little penetration on pellets for any armored target.

You could also just use slugs which do work great for self defense, but can easily kill your neighbor.