@ Bello & ryan_kalani -- The forend is a replacement that (in connection with the tube and follower) brings the total of U.S. made parts up to three, which allows you to extend the capacity without violating 922r. There is no added functionality.
@Rick Rope -- I’m pretty sure you need three U.S. made parts to comply with 922r. As I understand it, there are 2 issues with the pistol grip stock. One is that the collapsible stock is technically 2 parts, so you need to replace 4 specified parts of the shotgun with U.S. made parts (not an issue with the fixed PG stock or the field stock, which are each a single part). Two is that some jurisdictions limit the capacity of pistol grip shotguns due to their evil feature, which is not an issue where I live.
@d & John P. -- Thanks. “Riot gun” perfectly describes what I was trying to build.