personally I think there design with scrape off a lot of wadding. I have worked on shotgun suppressor designs with a someone I know. learned a lot on the designing the stack to keep from shaving the wad and preventing it from starting to open before exiting........
on a side note........a over and under suppressed would be cool.
while a pump action would be more practical, the over and under is kinda cool............a intergal design for my SBS would be sweet so I can keep it at 14.5" barrel length.