A linear seat belt pretensioner (10, 110, 210) has a frame (12; 112, 113; 212, 213) and an axial cavity (24, 60; 124, 160; 232) rigidly connected to the frame (12; 112, 113; 212, 213), a gas generator (20, 120, 220) in fluid communication with the axial cavity (24, 60; 124, 160, 232), and a piston (40, 140, 240) movably arranged in the axial cavity (24, 60; 124, 160; 232). An actuating profile (42, 142, 242) movable with the piston (40, 140) pulls a length of seat belt webbing (38, 238) into the frame (12; 112, 113; 212, 213) that corresponds to twice the piston stroke (D). The pretensioner device having a locking ramp arrangement (66, 70; 266, 290, 292) configured to form a one-way clutch allowing an increase and resisting a reduction of the length of belt webbing (38, 238) received by the pretensioner (10, 110, 210).