What is a characteristic of the M16 series rifle or M4 series carbine?

The M16 series rifle and M4 series carbine are specifically designed to be lightweight and efficient, which is why the correct choice highlights their 5.56-mm caliber alongside their gas-operated mechanism. The lightweight aspect is particularly significant in military applications, allowing for greater ease of use during prolonged carry and maneuverability in various environments.

The gas-operated system enables reliable cycling of the action, making it an effective choice for sustained fire. This design contributes to the rifle’s overall performance, allowing it to maintain a high rate of fire while minimizing recoil. The focus on the 5.56-mm round further underscores the rifle's ability to deliver effective stopping power with manageable weight, aligning with modern military combat requirements.

In contrast, the other options refer to characteristics that do not accurately describe the M16 or M4. For instance, these rifles are not known for being heavy and bulky, nor do they rely on manual cycling since they use a semi-automatic or automatic gas system. Additionally, both the M16 and M4 are magazine-fed weapons, which is a key aspect of their design enabling rapid reloading and sustained fire.