Abstract: A priming device for initiating explosive compositions. The device includes an elongated shell preferably formed of a synthetic plastic material which has a compartment closed off at one end for housing a sensitive explosive material which is more sensitive than the usual bulk explosive charges to be detonated. Also included in the primer unit is a passageway which is open at both ends of the shell for receiving and housing an electric blasting cap. This channel has an inwardly extending shoulder which reduces the inner diameter thereof but still permits the passage of a blasting cap therethrough. However when the cap and its leg wires are both laced through and lodged in the passageway the cap becomes wedged at the shoulder to hold it firmly in position within the device with the base charge end of the cap adjacent to the compartment containing the sensitive explosive material.