The Cobra CB38 Big Bore Derringer is a single shot pistol that fires the .38 special centerfire round.
One was used by Henry Merchant as a stand-in for a Remington 1866 Derringer. Henry originally confronted Emily Merchant with the weapon and held her at gunpoint, eventually shooting her, at which point she vanished through the Art Museum - Victorian Warehouse Anomaly. He followed her, and finding that she is accompanied by Matt Anderson, held Matt at gunpoint. The standoff ended when the Raptor ultimately saved Matt, just by killing Henry for good.