I guess it's all how you look it, to me a 273 bore is tiny, compared to that I see 318/360/340 bores being similar in size and all are tiny compared to 383/440/400 bores. A 3.98" bore would be half way between a 273's 3.625 and a 400's 4.34" bores so I see 318/360/340 as mid size bores.