An injection system includes a syringe and a plunger. A wiper sidewall of the plunger defines a cavity, into which a plunger shaft of the system is inserted, for moving the plunger, within the syringe, for fluid injection. The plunger includes a feature for engaging the shaft, and the sidewall preferably includes an expandable-contractible portion, in which the feature is formed. When the plunger is initially mounted within a first length of the syringe, the expandable-contractible portion of the sidewall is expanded and the feature of the plunger does not operably engage the inserted shaft. When the shaft moves the plunger into a second length of the syringe, the expandable-contractible portion of the sidewall contracts and the feature operably engages the shaft. An optional deformable end wall of the plunger may be spaced apart from a distal terminal end of the inserted shaft.
