The FBI forearms experts pretty consistently used the term Mannlicher-Carcano, so it's in a lot of documents and not that easy to get rid of.
On a related note, the pronunciation of Carcano isn't necessarily as straightforward as one might think. I've always put the stress on the second syllable, i.e. Car-KAH-no, because that sounded the most Italian to me, but it seems putting it on the first syllable is actually correct.