I wonder about how it feeds and ejects. Gotta wonder about the recoil in a 5 pound 20 gauge. Those are 450 marlin ballistics. I also wonder about penetration. Soft lead pancakes pretty fast at that speed,. I guess if you can only fire it in their barrels, Feeding is probably a done deal. Iagree, though, I don't see a need for the longer cartridge type, unless you are going a lot heavier inshot/slug weight than normal. You could just change your wad thickness otherwise.