Travis Haley of Haley Strategic demonstrates the Heckler and Koch MP7A1 from concealment:
https://www.youtube.com/watch?v=NfKDF2A7Djk
If you listen closely at the end of the video, when it speeds back up to real time, you'll hear the last round ring off the steel target. That was all 40 rounds on full auto on a steel target at 25m. The MP7A1 may be a niche weapon, but it sure is impressive for its size, weight, controllability and rate of fire.