Your Nagant has an unusual design, which pushes the cylinder forward to form a gas seal with the barrel's forcing cone. This makes it possible to somewhat effectively suppress this pistol. The original ammunition is a 7.62x38 crimped round, with the entire bullet seated inside the brass case. This crimped design also works toward sealing off the escape of gasses through the gap between cylinder and barrel. I believe an alternative round is the .32 Long, but original ammo is available:
http://ammoseek.com/ammo/7.62x38-nagant-revolver