A machine for modifying a sidewall defining a die cavity formed in a die with a slug retention groove comprising: a base grounding the machine to the die adjacent the die cavity; a slide arrangement carried by the base, the slide arrangement having a fixed slide block attached to ground and a movable slide block movably coupled to the fixed slide block for movement relative to the fixed slide block and the die cavity in a direction toward or away from the die cavity; and a machining head carried by the movable slide block for movement therewith relative to the fixed slide block and the die cavity in a direction toward or away from the die cavity, the machining head having a slug retention groove forming tool used to form the slug retention groove in the cavity-defining sidewall; a machining head motion limiter formed by abutment between a stop arm of the movable slide block and a stop landing of the fixed slide block that limits movement of the movable slide block, machining head, and tool relative to the fixed slide block and the die cavity in a direction toward the die cavity defining a maximum range of travel of the movable slide block, machining head, and tool; and characterized by a removable stop (180a, 180b, 180c) comprised of a plate having an abutment (208, 226) positioned between the stop landing of the fixed slide block and the stop arm of the movable slide block, against which the stop arm of the movable slide block abuts during travel of the movable slide block, machining head, and tool in a direction toward the die cavity to limit movement of the movable slide block, machining head, and tool relative to the fixed slide block and the die cavity toward the die cavity to a range of travel less than the maximum range of travel without the removable stop (180a, 180b, 180c) installed and in that the plate is position-adjustably attached to ground for enabling position adjustment of the stop (180a, 180b, 180c) relative to the stop arm and die cavity. a base grounding the machine to the die adjacent the die cavity; a slide arrangement carried by the base, the slide arrangement having a fixed slide block attached to ground and a movable slide block movably coupled to the fixed slide block for movement relative to the fixed slide block and the die cavity in a direction toward or away from the die cavity; and a machining head carried by the movable slide block for movement therewith relative to the fixed slide block and the die cavity in a direction toward or away from the die cavity, the machining head having a slug retention groove forming tool used to form the slug retention groove in the cavity-defining sidewall; a machining head motion limiter formed by abutment between a stop arm of the movable slide block and a stop landing of the fixed slide block that limits movement of the movable slide block, machining head, and tool relative to the fixed slide block and the die cavity in a direction toward the die cavity defining a maximum range of travel of the movable slide block, machining head, and tool; and characterized by a removable stop (180a, 180b, 180c) comprised of a plate having an abutment (208, 226) positioned between the stop landing of the fixed slide block and the stop arm of the movable slide block, against which the stop arm of the movable slide block abuts during travel of the movable slide block, machining head, and tool in a direction toward the die cavity to limit movement of the movable slide block, machining head, and tool relative to the fixed slide block and the die cavity toward the die cavity to a range of travel less than the maximum range of travel without the removable stop (180a, 180b, 180c) installed and in that the plate is position-adjustably attached to ground for enabling position adjustment of the stop (180a, 180b, 180c) relative to the stop arm and die cavity.