Again, you're theory is based upon a banned shotgun.
The M4 is not banned as imported yes, we agree.
The H2O is assembled by Benelli. I don't care what they have or have not done to it, 922R DOES NOT APPLY TO POSSESSION.
What don't you get?
Under 922r you are fine.
Here are the requested pics. It seems the mag tube probably has been replaced. However, it would look like that whether a factory or aftermarket tube was removed and or removed and replaced/coated.