Ruger does a lot of limited runs of special calibers for their distributors from time to time. Stuff like the .35 Whelen, 6.5x55, and 7.62x39 come to mind for ones recently (as in the last few years). I haven't checked the caliber availability on the website lately, but they used to chamber the Hornet and the .220 Swift as regular chamberings for many years in the #1B. Perhaps they dropped them, as they can't be the most popular of rounds in the #1.