The news media has recently portrayed assault rifles as an evil of society. However, the assault rifle is a misunderstood device. The M16, the standard assault rifle used by the United States military and many other defensive forces throughout the world, derives its popularity from its durability, efficiency, accuracy, and variable fire rate. The firing mechanism provides the user with the option to fire a single round, three rounds, unlimited rounds, or none at all. Many principles of physics are involved in the operation of the M16, including the dissipation of heat, the mechanics of the trigger assembly, and the feeding of the magazine. This article covers some of the basic design principles of the M16, describes how it works, and briefly explains its origins.
Introduction
The east coast sniper attacks of October 2002 sparked national apprehension of the gunman's weapon, a Bushmaster .223 caliber assault rifle. However, a well-known, military version of the assault rifle, the M16, has provided American soldiers with a precise and efficient weapon to protect the freedom of US citizens. Many engineering principles are endemic to the M16 rifle.
Creation
In 1954, the Armalite Division of the Fairchild Engine and Airplane Corporation in Costa Mesa, CA, was founded to develop military firearms using the most recent and innovative plastics and non-ferrous materials. Eugene M. Stoner, with the help of Robert Fremont and L. James Sullivan, developed the AR-15 (Armalite, Inc). Several studies conducted by the U.S. Army's Operations Research Office selected the AR-15 as the best small caliber weapon, and it was adopted as the M16. Therefore, the M16, AR-15, and Bushmaster .223 are all classified as assault rifles because they are similar in design and have the same capabilities.
The M16, often called "The Black Rifle", earned its popularity through its successful performance in a multitude of military environments, including arid, temperate, and arctic (Norris 61). The engineering behind the M16 is fascinating, simple to understand, and is based upon principles ranging from the physics of heat dispersion to the mechanics of loading and firing a single round. Although most Americans do not own an assault rifle, its underlying engineering can be seen in different applications of daily life.
Materials and Heat Properties
The M16 is created from durable materials that are able to disperse or resist heat. Every material has a heat capacity, which is defined as the heat energy required to raise the temperature of a substance one degree (Tipler 567). When the bullet moves down the barrel, some of the energy of the moving bullet becomes heat due to friction. From physics, we know that this generated heat diffuses throughout the whole rifle and the temperature increases relative to the heat capacity of each material (Tipler 542). Because of this property, the rifle is made of different materials that can endure high temperatures.
Under normal operating conditions, heat is kept to a minimum. Thus, though the barrel becomes hot, the handgrips of the rifle do not retain enough heat to burn flesh. One of the handgrips is even located on the barrel, but it does not heat up to a dangerous temperature because there is an air gap between the barrel and cover. This gap allows some heat to dissipate into the surrounding air instead of being transferred to the grip. The concept of heat is analogous to warming a pot on the stove. The bottom of the pan is heated and the heat disperses through the entire pan, including the handle. This explains why most handles have a covering, or are completely composed of a material that has a high heat capacity.
