My copy of Cartridge Conversions says it can be made from 7x57R. It says,
"Turn rim to .506"dia. and back chamfer.
Taper expand to about .315"dia.
Trim to length, chamfer and F/L size.
Fireform."

A fun cartridge that I used with Barnes 150gr flatpoint. Which was a large hollow point.
The FTX is a natural!

"Camping places fix themselves in your mind as if you had spent long periods of your life in them.
You will remember a curve of your wagon track in the grass of the plain like the features of a friend."
Isak Dinesen