N THE YEARS RIGHT AFTER WORLD WAR II, THERE WAS considerable interest in what we might call “sub-bore” cartridges, and that interest has persisted in varying degrees. For the purposes of this discussion, I’ll define “sub-bore” cartridges as smaller than .22 caliber, i.e., bore diameters less than 0.224 inch. Some commercial cartridges that fall into this group are Hornady’s version of the .17 K-Hornet, Remington’s .17 Fireball and .17 Remington, and the .204 Ruger, also from Hornady.
Of course, wildcatters have been busy, too. James Calhoon has developed .19-caliber cartridges called the .19 Hornet, .19-223, and .19 Badger on the .30-caliber M1 case. Another pioneering sub-bore experimenter was Bill Eichelberger, who developed rounds with .10-, .12-, and .14-caliber bores, including some rimfires. Early development of sub-bore cartridges was hampered by…