Pipe conveyed explosive with self contained actuation

A pipe conveyed charge system, for example a junk shot, having a self-contained activating charge which may be activated by mechanical force applied through the pipe. The initiating charge is pressure actuated, and fluid pressure in the pipe is used to fire the charge. The system includes a circulating crossover coupling an explosive charge to a pipe string and including circulating ports directing fluid flow downhole to clear debris from the borehole. A ball, or other blocking material, is conveyed down the drill pipe to block circulating ports to facilitate raising pressure in the pipe to a sufficient level to fire the activating charge.