Injection device fill volume management

An assembly for a firing mechanism for use in an injection device and comprising:

• a rear cap having an elongate member extending axially forwards when installed within the injection device;
• a plunger carrier releasably connected to the elongate member and fixed in position relative to the elongate member before release from the elongate member;
• a plunger releasably connected to the elongate member via the plunger carrier and, upon release of the connection between the plunger carrier and the elongate member, axially displaceable in a forward direction;
• and
• a plunger driver to drive the plunger axially forwards upon release of the connection between the plunger carrier and the elongate member, the plunger driver positioned between the rear cap and the plunger and received within the plunger such that a first end of the plunger driver abuts a forward end of the plunger,
• wherein the plunger and the rear cap define an axial length of the assembly, which in turn determines a start position of a forward end of the plunger before release of the connection to the elongate member,
• wherein one or both of the plunger and the plunger carrier comprises a plurality of connection features for connection between the plunger and the plunger carrier during construction of the assembly, the plurality of connection features defining a plurality of different positions at which the plunger is releasably connectable to the plunger carrier, each of the plurality of different positions defining a different start position of the forward end of the plunger,
• and wherein, during construction of the assembly, the plunger is releasably connectable to the plunger carrier at one of the plurality of positions defined by the plurality of connection features for controlling the axial length of the assembly and for defining the start position of the forward end of the plunger.