Until today, since 1986, Soviet/Russian cosmonauts have carried an interesting three barreled pistol / carbine / shotgun into space!

The Toz TP-82 has two side by side smoothbore barrels which fire 12.5mm shot shells and flares. The lower rifled barrel fires 5.45mm ammunition.

The removable stock can be used as a machete. The gun weighs 2.4 kg without the stock.

From Huntbl.ru (translated from Russian using Altavista Bablefish):

… underwent comprehensive tests in different climatic zones of the countries, which confirmed its high reliability and effectiveness under the extreme conditions. In the process of tests were obtained different forms behave like a beast and birds. From the threaded stem successfully they fired back moose, Kabanov, mountain goats, Gasella subgutturosa, saigas, foxes on the distances to 200 m, with the weight behave like a beast to 200 kg. from the smooth it is trunk they acquired hares, foxes, geese, weft, partridges, turtle doves, pheasants, seagulls.

I imagine the reason they combined a shotgun, pistol, carbine and flare gun was to save weight.

The weapon will not be used in the next space mission (12 October 2007) because the ammunition it uses has has run out.

I read about the gun here (the journalist who wrote the article knows very little about guns and ammo).