What does a spent casing indicate about a round fired from a firearm?

A spent casing signifies that the round has been fired and is no longer usable. When a firearm is discharged, the bullet exits the barrel and the casing is expelled from the firearm, indicating that the round has completed its intended function of being fired. This process is fundamental to the operation of firearms, as it allows for the next round to be loaded and fired. The spent casing typically bears marks from the firing pin strike and the chamber, which can also provide information about the condition of the firearm and the ammunition used. Thus, recognizing a spent casing is critical for understanding firearm operation and gun safety, as it signals that a round has been fully cycled and can no longer be loaded for use.