Abstract: A carrier for supporting a primer explosive charge in operative relationship to initiating means therefor comprises a cup having a recessed portion in its closed bottom end for engaging an explosive-containing plastic connecting block, used to explosively couple a low-energy detonating cord (LEDC), threaded through a tunnel in the cup, to a percussion-actuated detonator seated in a cavity (cap well) in the cup. A number of such primers can be made to slide on a single LEDC downline for placement in decked explosive charges in a borehole. Two tubular members project into the cup from the recessed portion, forming one or two cord-threading tunnels and a cap well. Besides initiation of a detonator by an LEDC downline via the explosive coupler, the carrier allows the primer charge to be initiated by a high-energy detonating cord or an electric detonator in an axial tunnel in the cup, or by a length of LEDC threaded through a tunnel and connected to a non-electric detonator seated in the cap well.