A bunch of rifles were cut down into carbine form for the NRA; I have one of those. It's identifiable by the Buffington rear sight combined with a front sight base that is mounted on a ring around the muzzle end of the barrel. (Factory carbines had sight bases integral with the barrel proper.
Interestingly, as time goes by, "NRA carbines" have come to be seen as collectable in their own right, if worth a fraction of the value of their true carbine counterparts.