Steve,
After pondering this one recently, I decided to go the route of a wildcat.
After doing a good month or so of research, I opted to try my hand with the .22 Super Jet.
It's ballistic's are "on par" with the .218 Mashburn Bee (also a wildcat), and is closely comparitive to the .221 Fireball.
My main reason...?..........two really...
It's based on the .357 Magnum brass (which I have a ton of), and it is a rimmed cartridge which is a little more preferred in the Encore single action in which it will be shot.
Dimensionally, the case is 20.16grs of water, in comparison to 21.77grs of water in the .221 Fireball case.
That being said, one big difference is the cartridge's shorter, fatter size, with a slightly sharper shoulder. A similar difference in comparison to the 22PPC in comparison to others.
Right now, based on the limited data that is available, the .22 Super Jet reaches velocities of up to 3300-3400fps using 45 & 50gr bullets and very light charges of Li'l Gun, H110, 2400, 4198 and 4227.
I've recently sent off a barrel blank and a couple of dummy rounds to Mike Sirois at "On Target Technologies" to chamber for me. He does a phenominal job on his barrels using EDM processes for chambering. Many report his barrels shooting 1/2" groups or less just shooting fireforming loads.
Based on all that, I've been asked, "why not just shoot the .221 Fireball and forego the pain of brass forming ?"
.221 Fireball brass is about $24.00 a 100.
.357 Mag Brass is less than half of that, and with a little case forming, you've got a case that holds 2/3rds the powder capacity of the .222, with approx. the same velocity.
From what I've read, accuracy is spectacular.
The "Super Jet" has also been known as the .22 Cotterman Jet (after it's originator), the 22/256, the .22 Ackley Jet., etc.
Although there is very slight differences between them, the load data, reportedly, can be used with all. Cases can be made from simply fireforming the .22 Rem Jet in a Super Jet chamber, necking down a .256 Win. Mag, or using the .357 Mag parent case, like I am.
I guess I'll have more to report when the barrel gets here........
If you opted to go this route, I'll give you any help I can, and moneywise, it's only slightly higher than a TC Custom shop barrel.
Just a thought.........or suggestion.
Take care,
Bob