The shotgun can be used as an auxiliary weapon when mounted under the?

The shotgun is designed to be mounted as an auxiliary weapon primarily on the M4 platform. This is due to the compatibility of the M4's rail systems and overall design, which accommodate the attachment of various accessories, including shotguns. The M4’s lightweight and modular features make it an ideal base for mounting additional weapons, thereby enhancing versatility and operational capability in the field.

In contrast, while the M16 and AR-15 share some characteristics with the M4, they were not specifically designed with the same level of accessory adaptability as modern configurations of the M4. The AK-47, being a completely different system with a distinct design and mounting capabilities, does not support the auxiliary use of a shotgun in the same way. Therefore, the M4's compatibility with auxiliary weapons like shotguns makes it the correct choice in this context.