Abstract: The longitudinal position of an inner barrel within a core barrel assembly can be adjusted and locked in the field without necessitating the disassembly of the cartridge cap assembly within the core barrel tool, and therefore without entailing loss of expensive rig time. The inner tube is coupled through a swivel assembly to a cartridge cap. The cartridge cap is threadedly coupled to the coring tool, and in particular to the outer tube. Thus, the cartridge cap is arranged and configured to be rotated, and thus longitudinally adjusted with respect to the outer tube. An upper portion of the cartridge cap is provided with a plurality of radially expanding fingers. A jam nut is disposed within a cylindrical array formed by the fingers, and is threadably engaged with the inside surface of the fingers.