squib shape charge and the percussion cap have to be aligned but no sealing means is needed and further the percussion cap can be used with force much more easily and accurately than the burst disk of the prior arrangement disclosed in fig1 through 3 also in this embodiment of fig4 through 6 the percussion cap 18a only needs to be misaligned approximately 10 or 11 degrees such as angle u03b2 as illustrated in order to safe the device and prevent shaped squib charge 24a from being effective in setting off percussion cap 18a referring now to fig7 and 8 another embodiment of this invention is disclosed that includes housing 10 with core 12 mounted relative thereto so that higher housing 10 or core 12 can be rotated relative to the other member to align percussion cap 18a mounted at the periphery of core 12 with a piston type squib 24b which has a piston 25a for striking percussion cap 18a and setting off side charge 16 and booster charge 14 to cause the rocket motor to be ignited also in this embodiment close tolerances between the inner surface of housing 10 and the outer surface 20a of core 12 is not required since a pressure type seal is not involved in this embodiment that is when it is desired to arm the device members 10 and 12 are rotated relative to each other to align piston 25a with percussion cap 18a when squib 24b is.