the prima cord is fired by an ignition connector 44 which connects the electrical bridge wire 20 to the firing end of the prima cord 42 the prima cord 42 is centrally located in the propellant pack 36 deviating only to connect to the detonator 46 at the end of each shaped charge grenade 26 where large diameter housings are used the grenades can be positioned such that the prima cord maintains a straight axial position throughout the fracing device the central location of the prima cord is important to initiate the radially outward burn pattern of the propellant the high velocity ignition of the prima cord provides virtual simultaneous detonation of all of the shaped charge grenades along the entire length of the fracing device the radial burn is important for several reasons i e it establishes the mass rate of burning per unit time as proportional to the radius r of the burn front and the mass of propellant burned as proportional to burn front radius squared r 2 further it eliminates any vertical thrust up or down well so that formation entry and fracing are precisely located together independent of device total burn time in end lighted propellant charges depending on the burn velocity the total burn time can be so large as to.