The .22 centerfire craze took hold around 1930, with the development of the .22 Hornet by Wotkyns and Woodworth who were engineer-types at Springfield Armory. They used a M1 Springfield (M1903 adapted to .22 rimfire), converted to centerfire. It was essentially a .22WCF but with hot-for-the-time smokeless powder instead of black, and a .223 bore and jacketed bullet. (.22WCF utilized a .226-.228 lead bullet) Strange that W-W started offering loaded ammo before any factory rifles existed for it- the Savage 23-D and Winchester M54 Hornets didn't appear until a year or two or three later. After that the shooting world went crazy for all manner of .22 wildcats based on about every small-medium capacity CF case available at the time, and a few more factory CF's to boot- all during that 10 year period before WWII.
Before that, like has been noted here, guys whacked varmints with anything that fell to hand but it wasn't a real sport as such among the general public, except for a few real rifle loonies who pestered guys like A.O.Niedner to build them .25 and .22 CF's on specialized rifles, more often than not with necked down .32-40 and .30-40 Krag cases. After the Hornet and all the rest of the bunch arrived in the 30's it became a real pastime for a whole lot of folks. As noted there were loads more groundhogs and prairie dogs to shoot at than there were deer, so for a lot of guys varminting became their main hunting pursuit.
Before the Hornet, pretty much all .22 work was with .228 bullets, as that was the diameter for all the .22CF's that came into being during the 1800's/early 1900's- .22 Maynard, .22-10-45, .22WCF, .22 Savage High Power, etc.
I just finished re-reading C.S.Landis ".22 Caliber Varmint Rifles", published 1946. If you want a fascinating read about the history and development of varmint rifles in the U.S., that's the book for you.
