With regard to the old knackered Stevens 311A 20 Gauge, it doesn't matter in the slightest what it looks like. Providing it works and a projectile comes out of it then it's fine for defence purposes.
I wouldn't like to be in it's way I can tell you...
Here in the UK we aren't allowed to cut shotgun barrels down to less than 24 inches. What's the law there in Yankland?