An improved detonator assembly for a black powder firearm having a breech block, a receiver, and a nipple. The detonator assembly comprises a primer and a primer carrier. The primer carrier has an axial bore dimensioned to receive the primer at one end and slip over the firearm nipple at the opposite end. The primer carrier has a lip that abuts the breech block rear end. A tab laterally extends from the lip to provide a handle for installing and removing the assembly and a visual indication that the firearm is primed.