Subcutaneous emphysema is often found in car accident victims because of the force of the crash. Chest trauma, a major cause of subcutaneous emphysema, can cause air to enter the skin of the chest wall from the neck or lung. When the pleural membranes are punctured, as occurs in penetrating trauma of the chest, air may travel from the lung to the muscles and subcutaneous tissue of the chest wall.
Both the Army and the Marine Corps teach that the maximum effective range of the M16A2/A3/A4 is 500 meters on a point target (individual enemy) and 800 meters on an area target (i.e. troops in the open).
If you put numbers like that into the equations, you'll find a rifle bullet, fired at an angle of 45Â°, ought to travel about 100â150km (60â90 miles) from the gun! Of course, bullets don't go anything like that far: the maximum range might be up to about 4 km or 2.5 miles.