It is the feeling/sound made when a case that has the body area just ahead of the web expand at firing and become very tight in the chamber. Upon extraction the bolt is raised until it starts on the extraction cam where is gets difficult to raise the handle more. When enough lift force is applied the handle snaps upward as the case pulls free from the chamber wall making an audible/palpable click. Sometimes it hardly upsets the gun but, if it is really tight, I have to 'pop' the handle up with my palm to get the case extracted. Hot loads cause this, with other associated pressure signs, in any chamber but mild loads can do it in 'fat cased' magnums using moderate loads. This occurs after a few firings when the die is not sizing that area enough. Solutions, as mentioned, can be a small base die, a new custom die based off your fired brass, or having your gunsmith open up the lower 1/4-1/3 of the chamber about 0.001-0.0015" with emery cloth on a dowel while the barrel is chucked in a lathe. In my experience, once the brass starts clicking after a few firings that area is hard to bring back down to an appropriate size due to work hardening. New brass is suggested in addition to the above measures to keep the new brass from taking that expanded set.