Concept semiautomatic shotgun. Was going to be pump-action, but the pump looked tremendously ugly. Tube magazine on top, barrel on bottom, bolt rotates and retreats backwards to eject spent shells downwards a la P90.
Also, the method you are using to eject spent cartridges will lower the recoil quite a bit. However, I think you should put a thumb guard there and have a longer ejection tube to prevent it from making contact with the operator's hand.