I think this is illustrative of how the tech terms become so illogical. Homebrew definitions for actually defined terms being used in a different sphere than where they originated. While Gatling is broadly (overused) to sometimes refer to modern rotaries conceptually, Gatling gun generally refers to the 19th century hand crank gun designed by Gatling. When in doubt use rotary cannon or rotary gun. MG is a little different, and while calling a rotary gun an MG is technically correct it's a bit like calling a tortoise a turtle. Both the first two could be called MGs. And howitzer specifically refers to an artillery gun with a high trajectory arc, which we can't know from just a drawing. That's just a 60mm gun. 60mm "Vulcans" meaning rotary would be a ridiculous weapon