a firearm safety device for installation into an otherwise functional firearm for disabling the firearm with respect to chambering and firing a round of ammunition and thereby enabling the firearm to be used as a training firearm . the functional firearm includes , among other items , a removable barrel that defines the bore for firing a round of ammunition . the replacement barrel is a unitary , solid structure wherein the portion corresponding to the barrel bore is closed , thereby preventing the chambering and firing of a round of ammunition . the replacement barrel is constructed and arranged to accurately and precisely simulate the size and shape of the removable barrel so that once the replacement barrel is installed , all other portions of the firearm remain functional . this enables other aspects of firearm usage and safety to be explained while , at the same time , providing an absolutely safe firearm that is not capable of firing a round of ammunition .