I believe the 62 was built in 30 carbine and 256 Winchester. I have heard that the 22 jet was done, but never seen one.
barrel is indeed pinned, but that can be updated surely. Get a barrel blank and put it on.
Running 357 mag brass thru a 30 Luger sizing die first helps to take a run at the 256 win sizing die.
I have pondered changing my 62 in 256 Win Mag to 22 Super Jet, but not done it yet. The 22/30 carbine sounds like fun to me.
