The heat of a bullet fired in midair comes from several sources, primarily the combustion of the gunpowder propellant within the cartridge and the friction with the air as it travels. While the initial heat from combustion is significant, it dissipates quickly. The primary source of heat during its flight is the result of air friction, known as aerodynamic heating.
Here's a breakdown:
- Initial Combustion: The firing pin ignites the primer, which then ignites the gunpowder in the cartridge. This explosion creates very high temperatures and pressures, which propel the bullet forward. This initial heat is primarily concentrated in the barrel and the cartridge case and is quickly transferred to these components. The bullet itself gains some initial heat, but it's not retained for long.
- Aerodynamic Heating: As the bullet travels through the air at high speeds (often supersonic), it experiences substantial friction. This friction converts the kinetic energy of the bullet into heat. The higher the bullet's velocity, the greater the friction and, consequently, the higher the temperature. However, this heat is usually confined to the surface of the bullet and doesn't significantly increase its core temperature.
- Factors Influencing Heat: Several factors affect how hot a bullet gets during its flight. These include the bullet's velocity, the shape and material of the bullet, the air density (which varies with altitude and temperature), and the distance traveled. Faster bullets experience more intense aerodynamic heating.
- Temperature Range: While it's difficult to give a precise temperature figure, the surface of a bullet can reach hundreds of degrees Fahrenheit due to aerodynamic heating, particularly for high-velocity rounds. However, the bulk of the bullet's internal temperature increase is relatively minimal and short-lived. It is important to understand that the heat will largely dissipate quickly after the bullet exits the gun barrel.
In summary, a fired bullet's heat is primarily derived from the initial combustion, with aerodynamic friction being the dominant heat source during its flight. Although the surface temperature may rise considerably, the bullet's overall heat is not excessively high, and this effect is not significant for most practical purposes.