An advancing/retracting mechanism having a pair of cams is disclosed. The advancing/retracting mechanism includes a first cam (22), a second cam (24), and a barrel (26). The first cam includes an angled surface (30) and a shoe (36), and the second cam includes an angled surface (52) and a slider (58). The shoe engages with a helical surface (42) in the barrel, and the slider engages with a straight surface (60) in the barrel. The first cam travels a first distance along the longitudinal axis of the barrel from a first to a second state, and the second cam travels a second distance that is greater then the first distance along the longitudinal axis of the barrel from the first to the second state.
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