Could the length be a rifle guy in a shotty world?
Ok so why not a weld on shell that has internal threads tapped in it?
(Please steal my idea)
The outer cage would come with an appropriate pilot for the barrel you are using. Cut your barrel, slip on cage and weld it on. Unscrew pilot and install any variety of chokes, flash hiders, compensators with any design of porting, barrel extensions, golf ball launchers, you name it, all fit to the weld on cage. Link soon to idea behind it