A device configured for insertion in the barrel of a shotgun for firing a rimfire ammunition round, and in particular, a .22 magnum rimfire round, in the shotgun. The device includes a carrier defining a bore that receives at least one rimfire ammunition round and a spring-biased extractor connected to the carrier and constructed to automatically withdraw a rimfire ammunition round from the bore upon the action of the shotgun being opened. The present invention may also include the spring-biased extractor being configured to automatically move to a retracted position relative to the carrier upon the action of the shotgun being closed and to automatically move to an extended position when the action of the shotgun is opened.