I do my job right after I was fired. What am I?

This riddle cleverly uses the double meaning of the word "fired." In one sense, to be "fired" means to be dismissed from employment. In the context of a projectile, however, "fired" refers to the forceful expulsion from a weapon, such as a gun. A bullet sits inert within a cartridge until the moment the primer ignites the propellant, typically gunpowder, creating rapidly expanding gases. This intense pressure is what "fires" the bullet, propelling it down the barrel and out of the muzzle at high speed.

Immediately after this powerful launch, the bullet begins its journey toward a target. Its "job" is to travel through the air, maintaining stability due to rifling grooves inside the barrel that cause it to spin, and then to impact its intended destination. This entire process, from ignition to impact, happens in a matter of moments, showcasing how the bullet performs its function directly following its energetic expulsion.

The concept of a bullet has evolved significantly over centuries. Early firearms used simple round lead balls, which were hand-cast and loaded with black powder. A major advancement came in the mid-19th century with the Minié ball, a conical projectile that expanded to grip the barrel's rifling, vastly improving accuracy. Today's bullets are precision-engineered, often featuring lead cores encased in copper jackets and aerodynamically shaped tips to enhance their flight and terminal performance. While the term "bullet" colloquially often refers to the entire cartridge, it is technically just the projectile component.

Therefore, the riddle works because the projectile is "fired" from the gun, and then, in its subsequent flight and impact, it performs the very task for which it was designed, perfectly fulfilling its "job." This linguistic play highlights the dynamic action of the bullet, making it an engaging and accurate answer.