According to "A Practical Grammar for Classical Hebrew" by Jacob Weingreen, page 19, the four gutturals are ALEF (א), HEI (ה), CHET (ח), and AYIN (ע). And gutturals make a difference as to vowels on the article HA- preceding nouns, and impacts what makes verbs irregular.
But CHAF (כ) (KAF with the dagesh lene omitted) is pronounced very similar to CHET.
Any ideas why it isn't considered a guttural? Is it because it has the two forms, KAF (כּ) and CHAF (כ)?