A magazine-indexing mechanism for a powder-actuated tool, of the type adapted for use with a disk-shaped cartridge magazine (15), is actuated by the same trigger displacement as actuates the firing mechanism (9). A first link (41), pinned to the receiver (1), and a second link (47), pinned to an extension (49) of the trigger (13), are pinned together, with a magazine-engaging hook (55) disposed on the distal end of the first link (41).
When the trigger (13) is pulled to fire the tool, the hook (55) is displaced to engagement with the magazine (15). When the trigger (13) is released, the engaged hook (55) is displaced, indexing the magazine (15). Means (45) are also provided to prevent indexing an unfired cartridge through the tool.