Since the n16 refurbish is a lame duck; its just a frame and some money for some extra damage and a +5% precision bonus (and the magazine becomes curved for some reason), I had a genius idea and I can't believe I didn't think of it sooner. With heavy duty installed, the refurbish could add an m203 ("n203" I guess) to the rifle and give it an option in the invoker to fire its single loaded grenade. M203's are 40mm. Not sure what all parts it would need; a short 40mm barrel for sure. The holes in the handguard are kino btw and should be added to the guns icon.
