517 391 filed oct 23 1974 is comprised of separable members 28 and 29 which can be disengaged from one another by manipulation of a common fishing tool with an ordinary wireline 20 or with uphole tubing pressure as will be more fully understood later on in this disclosure a jet perforating gun 30 made in accordance with the present invention is provided with an actuating shaft 32 which causes a firing head 33 to detonate the various shaped charges associated therewith upon impact of the actuator with fixed abutment member 34 an anchoring device 36 affixes the abutment member at a predetermined location downhole in the borehole so that the shaped charges when detonated perforate the casing adjacent to a hydrocarbon producing zone 38 a moderate temperature zone 39 exists uphole in the borehole where temperatures are below the boiling point of water further downhole there exists a high temperature zone 40 often in excess of 400 u00b0 f wherein ordinary electrical components and explosives associated with jet perforating guns cannot safely endure if permitted to reach equilibrium therein in the hypothetical representation of fig3 the temperature decreases at 44 as one penetrates the surface of the earth where the temperature remains fairly constant at 45 and then begins to increase at a more rapid rate at 45 39 the temperature continues increasing at 46 to define the upper limit of the before mentioned moderate temperature zone 39 whereupon the temperature continues to increase as one travels downhole until the before mentioned high temperature zone 40 is encountered in the claims the term 34 relative low temperature 34 is intended to define a temperature at which perforating gun components such as shaped charges prima cord blasting caps and electrical.