Assembly (39) for a bolt action firearm comprises impact member (43) for impacting firing pin (42), spring (44) and shroud (45) for housing both member (43) and spring (44). Shroud (45) connects to the proximal end of bolt (40) which houses firing pin (42) and firing pin return spring (41). When assembly (39) is in a firing mode, a firing mechanism controls the release of energy stored in spring (44) so that member (43) impacts on the proximal end of firing pin (42) which then fires a cartridge located within a firing chamber in a known manner. Firing pin (42) may be located in a concentric position relative to the axis of bolt (40) for firing centre fire cartridges, or the axis of firing pin (42) may be offset to suit rim fire cartridges.