When completing a well with a through tubing type perforating gun, it has heretofore not been possible to backsurge the perforations with more than a few hundred pounds per square inch differential from the formation toward the wellbore.  This is because the more desirable higher surging pressure will blow the gun uphole, thereby tangling the cable and causing extreme difficulty in removing the gun and cable from the wellbore.  Several thousand pounds per square inch differential pressure is required to properly backsurge perforations sufficiently to completely remove debris and compaction from the perforations as is done for example by the tubing conveyed system of completions, Vann U.S. Pat.  No.  3,706,344. 
It would be desirable to have made available a wireline operated through tubing perforating gun which can be employed for completing a wellbore and which further includes means by which the gun is prevented from being thrust uphole when the perforations are surged with several thousand pounds per square inch differential.