A firearm safety device purposed to obstruct the chamber of a firearm to block insertion of a cartridge therein, effectively disabling the firearm. In embodiments, the firearm safety device comprises a plug and a key. The plug may be sized for fitting within the chamber of essentially any firearm. The plug may be inserted into and removed from the firearm through the breech end of the chamber, thereby lessening both wear on the plug and potential damage to the firearm resulting from plug insertion or removal. The key interacts with the plug for easy positioning of the plug within the chamber and pulling removal of the plug out from the breech end of the chamber. Unauthorized removal of the plug is difficult without the key. The safety device enables repeated cycling of the action and dry firing of the firearm enabling the firearm to be handled safely for uses such as for retail sale purposes and for firearm use and safety training.