A manually-actuated slide-action handle (22) for a semi-automatic firearm. The handle has a chassis portion (58) and a length-adjustable shoulder stock portion (60) to enable a user to alter the trigger pull length of the firearm. A finger rest (82) stabilizes the end of a user's trigger finger stretched in front of the firearm trigger. The finger rest is detachable from the chassis and has a generally U-shaped configuration that is adapted to connect to the handle in either a right-handed position or an inverted left-handed position. A lock switch (116) is located on the grip base of a pistol grip feature (66) to selectively arrest relative sliding movement between the firing unit and the handle. A brake (76) is controlled by an engagement lever to selectively remove play between the handle and the firing unit portion of the firearm for competitive slow shooting.