A 32-year-old man is brought to the emergency department following a gunshot wound to the left chest. On examination, he has a single entry wound over the left anterior axillary line at the 5th intercostal space with minimal external bleeding. The exit wound is noted over the left posterior axillary line at the same level, with beveling of the skin edges. Chest X-ray shows a pneumothorax and pulmonary contusion. Which of the following features of the exit wound is most characteristic and helps differentiate it from the entry wound?