A magazine insert for a pneumatic tube conveyor capsule for receiving sample tubes filled with bodily fluids includes a magazine drum, a fastening unit, a slider and a catch element. The magazine drum has a plurality of receiving chambers for the sample tubes. The fastening unit is pivotable about the longitudinal axis from a fastening position to a release position. The slider in the central recess of the magazine drum is slidable in axial direction from a first functional position bidirectionally to a respective second functional position relative to the magazine drum. The catch element is fastened to the slider and extends in radial direction into a control cam of the fastening unit. A pivoting of the fastening unit from the fastening position to its release position can be effected by transferring the slider to its corresponding second functional position.