Stopping power is the ability of a weapon – typically a ranged weapon such as a firearm – to cause a target (human or animal) to be incapacitated or immobilized. Stopping power contrasts with lethality in that it pertains only to a weapon's ability to make the target cease action, regardless of whether or not death ultimately occurs. Which ammunition cartridges have the greatest stopping power is a much debated topic. Stopping power is related to the physical properties and terminal behavior of the projectile (bullet, shot, or slug), the biology of the target, and the wound location, but the issue is complicated and not easily studied. Although higher-caliber ammunitions usually have greater muzzle energy and momentum and thus traditionally been widely associated with higher stopping power, the physics involved are multifactorial, with caliber, muzzle velocity, bullet mass, bullet shape and bullet material all contributing to the ballistics. Despite much disagreement, the most popular theory of stopping power is that it is usually caused not by the force of the bullet but by the wounding effects of the bullet, which are typically a rapid loss of blood causing a circulatory failure, which leads to impaired motor function and/or unconsciousness. The "Big Hole School" and the principles of penetration and permanent tissue damage are in line with this way of thinking. The other prevailing theories focus more on the energy of the bullet and its effects on the nervous system, including hydrostatic shock and energy transfer, which is similar to kinetic energy deposit. History The concept of stopping power appeared in the tail end of the 19th century when colonial troops (including American troops in the Philippines during the Moro Rebellion, and British soldiers during the New Zealand Wars) at close quarters found that their pistols were not able to stop charging native tribesmen. This led to the introduction or reintroduction of larger caliber weapons (such as the older .45 Colt and the newly developed .45 ACP) capable of stopping opponents with a single round. During the Seymour Expedition in China, at one of the battles at Langfang, Chinese Boxers, armed with swords and spears, conducted a massed infantry charge against the forces of the Eight-Nation Alliance, who were equipped with rifles. At point-blank range, a British soldier had to fire four .303 Lee-Metford bullets into a Boxer before he stopped charging. U.S. Army officer Bowman McCalla reported that single rifle