What is a common feature of tracer rounds?

Tracer rounds are designed with a specific purpose: to provide a visual indication of the projectile's trajectory in flight. This allows shooters to track the rounds during firing, facilitating adjustments for better aim and more effective targeting in real-time. The visible trace can help in both training scenarios and combat situations, as it allows gunners to see where their rounds are impacting relative to the intended target. This functionality is the primary distinguishing feature of tracer rounds and highlights their utility in enhancing accuracy and effectiveness during weapon operations.

Other options, while they may represent different characteristics of ammunition types, do not encapsulate the defining feature of tracer rounds as effectively as the role they play in tracking and targeting.