How about a 22 center fire like this one as a commercial round
The 22 CCM around 1900fps from a 18" barrel with a 40 gr bullet
IN fact J and K frames set up with a dual firing pin and switching hammer like a model 53 22 jet with 2 cylinders would be nice if we are going to wish big. I have a model 53 and would "only" need a long cylinder, a bunch of brass and dies. The brass is unobtainium, but can be made from hornet brass with a bunch of work, which isn't all that easy to get either