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The RG-6 m209, called the Bulldog 6 m209, is a unique weapon featured only in S.T.A.L.K.E.R.: Shadow of Chernobyl.
The English in-game description is as follows:
A variation of the revolving granade [sic] launcher. The given model is made especially for use of granades [sic] of the western model.
AppearancesThe RG-6 m209 appears only in Shadow of Chernobyl. Neither S.T.A.L.K.E.R.: Clear Sky nor S.T.A.L.K.E.R.: Call of Pripyat feature a standalone grenade launcher which uses m209 grenades, nor any method of modifying a grenade launcher to use that ammunition.