An adjustable barrel, a barrel-adjustment assembly, and an adjustable distal tip assembly. The barrel is radially adjustable between an expanded position and a contracted position having different diameters. The barrel-adjustment assembly includes a barrel cam, a gear-set, and a rotary adjustment ring. The barrel cam rotates to unwrap and wrap the barrel thereabout between the expanded and contracted positions. The gear-set rotationally drives the barrel cam. The adjustment ring can be longitudinally translated from a disengaged position to an engaged position. In the disengaged position the gear-set is disengaged (but an anti-rotation assembly is engaged) and in the engaged position the gear-set is engaged (and the anti-rotation assembly is disengaged). Once in the disengaged position, the adjustment ring can be rotated, which causes the engaged gear-set to rotate the barrel cam, which in turn wraps and unwraps the barrel about the cam into increased or decreased diameters.