Did you watch the film Kingsman: The Secret Service? In the film, the Kingsman Agents use a modified Russian Tokarev TT-30 pistol. The prop master added a shotgun barrel. It was never used in the film but it was explained that it can shoot shotgun shells. Do you think it could work? It would be interesting to see a working version. But I do not see how you could fit a working firing pin in such little space.
Here is a picture of a stock Tokarev TT-30 for comparison.