Devices and methods for altering a firearm to prevent firing of rounds of a first size while allowing the firing of rounds of a smaller, second size are provided. In one embodiment, a barrel safety device prevents a live round from fully chambering in a firearm, while allowing a blank to be chambered and fired from the firearm. The barrel safety device includes a muzzle block, a rod, and a tip in one embodiment. The rod and the tip can be sized so as obstruct a portion of the barrel and/or the bullet chamber of the firearm, such that a round having a first length, such as a live round, contacts the tip of the barrel safety device and cannot be fully chambered. The rod and the tip can be sized so as to allow a cartridge having a second, smaller length, such as a blank cartridge, to be fully chambered without contacting the tip of the barrel safety device.