It can be done with a Dremel type tool. But that takes some patience and Dremel type skill!

I'd make a copy of the 9.5 cartridge on the Lathe. Then make a 'D' reamer out of it,,heat treated of course. These simple single cutting edge reamers are simple to make and cut beautifully but rather slow.

The reamer must be made so that it has a support extension made on both ends. One for driving the reamer and the other end for center/tailstock type support if needed.

The orig magazine follower cartridge flutes would be milled to the new dimensions with this D reamer by coming down into each flute from the top,,full length cut all at once.
Slowly advancing into the old flute, the reamer will start cutting the neck and shoulder portion first, then the cut away for the bullet nose clearance. Then finally the body portion of the reamer will make contact with the existing cut in the rotor.

At that point, the old flute has been recut to the new cartridge dimension.

It can be done on a Lathe or a Mill but will take some careful set up and positioning each flute.
Cut very slow, slow speed and feed and plenty of quality cutting oil.
A solid no vibration set up is needed for success.

It ain't fast, but a nice professional looking job can result.