I've seen cum used in Indian English pretty often in its Latin meaning, as in "with" and used often to mean something that serves multiple purposes. So this is talking about some kind of tank ammo which penetrates and blasts (presumably armour).

It was also used in other dialects of English as well, and we still have Latin phrases like "magna cum laude" (meaning "with great honour"), but some other meaning of the word has become more prominent...