Mysterious Super Long Revolver

This photo of a chap in the uniform of Brazil’s Polícia Militar do Distrito Federal (PMDF) holding a strange super long revolver has been appearing recently on social media. On the wall behind him is what looks like the coat of arms of a municipality, but I have not been able to identify it. The photograph seems to have originated from one of those Russian-language “cool photo” sites that publishes images entirely without captions or explanations.

My source: All Outdoor.