TinkerDave,
Some years ago when I couldn't find enough ammo for my Ruger 256 Hawkeye, I machined a brass insert for the chamber and shot readily available 25-20 ammo. Now I reload 256 for the Hawkeye.
Then it occurred to me that 25-20 would make a great round for a single six size Ruger, albeit too long for the cylinder. I didn't want to get into a custom longer cylinder. So I shortened some cases and loaded them. What I liked was that they cycle and shoot well in my Winch 25-20 carbine. So I could use the same round in both handgun and rifle.
Shortening the neck flutes on the 25-20 reamer and re-chambering an extra 22 Mag cyl is a cake walk. By using it in a 32 Mag SS, I didn't have to convert the firing pin to centerfire. I just need a .256 piece of barrel now to complete the gun. I may have to resort to having a 22 barrel re-bored to .256" but I don't have the $200 right now. I see now that what I came up with is similar to the .257 Jackrabbit on the single action website.
The 22 hornet seems like it would adapt to the short SS cyl. but I'm afraid too much case capacity would be lost because it's even longer than a 25-20. But I guess you picked the hornet for it's .22 bore, that sure simplifies the conversion and keeps cost to the price of a reamer; under $100 from Brownells. And again, a .32 mag ss w/centerfire firing pin makes it simple with just a barrel change to .22.
Now I'm thinking the 25-20 shortened and necked down to .22 would be the easiest conversion but I couldn't shoot it in my 25-20 rifle. In affect I'd have a .218 BEE with shorter neck and shorter case body. Shortening a 218 case would leave very little neck. So I'd start with a 25-20 case and have a 22-20 Ruger!
I have converted a .22 SS to centerfire which is quite simple using all the original parts, just relocating them. I converted an OM SS .22 to .32 Fed Mag for a friend who wanted one with the old 3 screw action. Started with a .32 H&R Ruger cyl and it's just barely long enough for .327 FM, and a Ruger .32 NM barrel:
Had to enlarge the loading gate chute slightly for the larger diameter cases.
Full details here: http://www.rugerforum.com/phpBB3/viewtopic.php?f=3&t=169381