Someone told you wrong. Hornets have been .224 for most, if not all my life, and I’m pretty old.
EDIT: A quick trip to Duckduckgo Land indicates that Hornets made since the war (WWII) are .224. Originals and lots of converted .22s from the bad old days are usually .223.
The .22 Jet was .223, probably to facilitate the use of .22 ammo in inserts.
Find another source of “information”.
