As Eric has noted, a small tab soft soldered to the rear end of the entry pipe extension, and filed with a downward angle can be fitted into the bottom of the inlet so that it retains the tail from popping up. I do this on all my entry pipes. This little tit can be added too, to the back end of a trigger plate, so that a rear screw isn't required. And on the end of a trigger guard for a pistol...as you can see, the list goes on and on. Nezxt time I take my entry pipe out of this current Western PA rifle I'm doing, I'll take a photo and post it.