Edit - I found out this rifle is .44 Long rimfire, see below.
I'm sure very few people are interested in making this cartridge. But I wanted to post it for someone in the future who may have a need for it.. In a nutshell, these are the steps I use.
I use 44 magnum brass. I'll tell you up front, making .46 long reloadable rimfire brass is a lot of work and not for the casual reloader. Here are the steps I've developed to convert the brass to rimfire.
1. Make a brass plug to fill the centerfire primer pocket. Solder this plug in place. Then face it in the lathe flush with the case.
2. Center punch a spot at the edge of the original primer pocket. This will be the where the plug and hole meet.
3. Drill the new primer hole. I start with a small drill fitted to the center punch spot. Then follow with a #2 drill.
4. Ream hole with a .224” chucking reamer for a slight press fit of the empty .22 blank.
5. Use a 9/32” drill bit (or end mill) to make a recess for the .22 blank rim in the new primer pocket. Test fit a .22
blank until the .22 rim is .003” - .005” below the .32 case rim.
6. Mill or file a firing pin relief slot about .016” deep in the case rim. This allows space for the firing pin to crush the .22 blank rim.
7. Clean up burrs and wash.
8. Trim to length. .46 Long is 1.250”
9. Size in a .44 mag die.
10. Anneal the case neck.