The tough part of scaling is reversed from making the real thing. There are several diminutive caliber & cartridge combinations, very few with the right proportions. Common for military arms; they build around known or approximated ballistics.
If one was to re-scale a .50 cal M2, .30-06 would be a candidate, being almost perfect ratio of reduction. Handgun calibers have few such parallels. https://en.wikipedia.org/wiki/3_mm_caliber