Gap creation device

A plunger assembly 100 for use with an auto-injector and comprises a cartridge 102, and a firing assembly 103 that includes a plunger rod 104 and a drive portion 105, the firing assembly being axially moveable relative to the cartridge. The firing assembly is configured to couple to the cartridge at a coupling point along a length of the cartridge to fix an axial position of the drive portion relative to the cartridge and wherein the length of the cartridge is configured to be extended in a rearward direction such that the coupling point and a forward end of the plunger rod move rearwards. The cartridge may comprise a first portion (122, fig 4a) and a second portion (124, fig 4a) axially moveable relative to the first portion for extending the length of the cartridge rearwards. Other plunger assemblies are also disclosed where the axial length of the plunger assembly is fixed and at least part of the cartridge moving rearwards. The arrangement prevents spillages due to expansion of medicament