What is the nomenclature of the M777A2 cannon tube?

The correct nomenclature of the M777A2 cannon tube is M777. The M777A2 is an upgrade to the original M777 design, but it retains the M777 denomination for its cannon tube. The "A2" designation specifies the variant of the M777 system that incorporates improvements such as enhanced digital fire control and the ability to use various ammunition types more effectively.

The M776 and M776A1 options represent other designs unrelated to the M777 family. M138A2 also refers to a different weapon system that does not pertain to the M777 cannon tube. Thus, recognizing the correct nomenclature as M777 ensures clarity and accuracy in identifying the weapon system being discussed.