and deep to accommodate radial extraction of the lower latching dogs 50 from a radial engagement with the latch collar 51 when the channel 58 is axially aligned with the base of the latching dogs 50 under in running conditions of gun placement the latching dogs 50 are laterally and circumferentially confined within windows in the caging sleeve 61 radially the latching dogs 50 are confined to the expanded position by a shoulder portion of the latching piston 54 when the latching piston is appropriately aligned the latching piston shoulder portion has a greater diameter than the root diameter of channel 58 in running the latching piston 54 support location for the radially expanded position of the latching dogs 50 is secured by shear pins 56 the upper end of the stinger element 23 is secured to an interventionless firing head ifh 27 a detonation cord channel 14 extends from the ifh along the length of the stinger 23 to the gun 24 detonator not shown detonation cord ignition occurs in response to pressure pulse signals transmitted along the well fluid from the surface the detonation cord channel 14 is vented at 66 against the lower ends of the latch piston 54 when the perforating gun is discharged combustion gas pressure is channeled through the vents 66 against the lower edge of the latch piston 54 this combustion gas pressure displaces the piston 54 to align the channel 58 under the lower latching dogs 50 and allow retraction of the dogs 50 from a meshed engagement with the socket cylinder latch collar 52 when the dogs 50 are retracted from the latch collar 52 weight of the gun unit.