The Finn's, and Scandinavian countries in general, have a longstanding tradition of loading, "Gallery Loads" for indoor shooting in winter, and training new shooters. Of course Gallery Loads were much more common in the late 1800s and early 1900s as public shooting events were considered a normal part of life.
One of the methods that has been used over the years is to find a lead ball of the approximate diameter of the bore (such as #1 buckshot for a 30 caliber rifle) and load it into with a very small charge of fast pistol powder. The 7.62x54r loaded with such "cat sneeze" gallery loads was described here:
http://guns.connect.fi/gow/arcane1.html
Jimro