What is the main goal of the M16 series rifle or M4 series carbine design?

The main goal of the M16 series rifle and M4 series carbine design is to provide lightweight and effective firepower. This design ethos emphasizes the need for a weapon that is easy to carry for soldiers while still delivering reliable stopping power and accuracy in a range of combat scenarios.

The lightweight construction allows soldiers to maneuver effectively on the battlefield, which is critical in various combat situations. The effectiveness of the firepower stems from the weapon's caliber, design, and rate of fire, making it suitable for both semi-automatic and automatic engagements. This combination of reduced weight and high effectiveness has made the M16 and M4 platforms highly adaptable to the needs of modern infantry.

Other options, while they highlight specific features or use cases, do not capture the primary design intention as fully as the focus on providing an optimal blend of lightweight convenience and effective combat capability.