You could do the 357 0n a 30-30 case. Like a short 357 Herret. The Longest possible cylinder would of course be best. I kind of want to do something using a .308 bullet. Except for the odd 30 carbine Ruger you never see a 30 cal. hand gun with any power.
Here is what I am thinking so far. Turn the stock to N cylinder OD. Drill and ream the center out of it. Turn an old N frame cylinder down and "harvest" the center piece that aligns the star and the back of the yoke rides against and shrink fit that into the new cylinder. Save broaching in the little tooth that keeps the ejector from turning when ejecting. Then I could fit an spare 357 star to new piece. Drill and ream pilot chambers on my mill using index able rotary table to hit every 60 degrees. Make a dummy barrel and a alignment tool. Install cylinder and dummy barrel in a frame. Then using dummy barrel and alignment tool align each chamber pilot hole and Use a modified cylinder stop to mark each chamber spot for its notch. Plus, I would set my rotary table up so its jaws were horizontal and use a keyway cutter to make the stop notches every 60 degrees using chambers and marks I made to cut slots using a dial indicator to check depth by how much I move table while cutting. Ream to wildcat chamber using custom reamer which you can order made up from Clymers.
I would use 4140 that is already heat treated to yield strength. It is still very machinable after HT and then no worries about distortion after HT. You can order it online, but, industrial B16 stud material is the same alloy and HT and next time I am in a refinery I will just scrounge some 1 1/2 B16 studs. I am sure this will test my patience and abilities.
So many projects, so little time. Well there is time, but once you take away honey does, the odd actual job, now and again, hunting, fishing, camping, napping and stuff its hard to do everything a guy would like to do. At 67 it bugs me that I probably only got another 20 to 30 years to get it all done. Right now I have an XP100 with the barrel removed so I can cut down and install a spare Mohawk 600 6mm barrel on it. It was a 7mm BR. But, I have enough calibers and already reload for my 6mm rifles. I bet this one will wake up everyone on the firing line.