A weapon with a telescoping bolt (also known as an overhung bolt) is one with a bolt which telescopes over, that is, wraps around and past, the breech end of the barrel. This feature reduces the required length of a weapon such as a submachine gun significantly, and it allows rifle designs to be balanced around the pistol grip in a way that gives "pointability" similar to a pistol's.
A telescoping bolt is an expensive modification for gun enthusiasts.
( z1 modify :ARG1 ( z2 bolt :ARG0-of ( z3 telescope ) ) :mod ( z4 expensive ) :beneficiary ( z5 person :ARG0-of ( z6 enthusiastic :ARG1 ( z7 gun ) ) ) )