I wrote once before about forming brass from one cartridge to make brass for another, but this one gets a bit more involved than most.
Meet the .310 Cadet
You will probably have to thin the case rim.
You will have to full-length size the brass in a suitable die.
You will have to trim it to length.
It uses an odd bullet.
So, where to start... my process was to
Resize the cases,
Thin the rims,
Cut to just above finished length,
final trim and deburr.
Friend had a set of .310 dies, so lubed the cases, pulled the deprime/neck expander assembly and resized the brass. I've read it can be done in a .30 Carbine sizing die, will have to try that sometime. Reason for resizing first is .32-20 is a necked case, and I wanted the straight body to fit into the lathe chuck.
I've read of people clamping the case in a drill press and using a file to cut the rim down. It should work, but that'd be a long way to do it. If you have access to a lathe, I'd suggest that.*
This being a somewhat worn little lathe, it took some fiddling to get the procedure right. That was stick the case into the chuck; use a caliper to set each case with the same amount sticking out;
use a facing bit to cut away at the front of the rim
until had a thickness of .046-.050", which proved to work nicely with the rifle in question.
To trim, I used a small Harbor Freight cutoff saw(originally bought to make .300 Blackout cases from .223). Took a piece of hardwood dowel, sanded it to a slip-fit in the case, adjusted it in the vise so it would cut at the right length
and went to it. Two things:
First, it took two cuts: the first to get rid of about half the length, the second to make the finished length.
Second, you have to hold the saw in position with one hand and rotate the case with the other, and you will make a cut into the dowel. But it gives you a pretty consistent length with minimal deburring needed. Which is good, because the walls of these cases are thin.
Note: if I were going to make a lot of these cases, I'd get a piece of aluminum rod, turn it to fit, and use that for the mandrel.
Trimming to exact length is tricky primarily because there are different lengths listed. I found this on one loading site
and that Kynoch cartridge up at the top measures 1.120", so I went with that.
.32-20 case sized, rim thinned, cut to length
For the bullet, RCBS makes a mold to cast the proper heeled bullet at a nominal 120 grains, and friend has one. These were used as-cast(15-1 as that's what was in the melter), and tumble-lubed with this modified Lee Liquid Alox.** Some searching around found a variety of loads, the primary for starting off seems to be 4.0 to 4.5 of Unique; this being a new one to me, I started with 4.0.
Original and new cartridge
They were tried out over the weekend; all went bang, accuracy seemed quite good
The case mouth was not crimped onto the heel; the die won't do that, so these were a tight press-fit into the neck. After having been fired the cases were formed to the chamber, and the bullet can be seated by thumb pressure. I'd hate to carry them out hunting that way unless in some suitable case, but it seems to work well for general target shooting.
There was no sign of leading or other nastiness in the bore, so the lube did its job. And I think this counts as success.
I'll have some more on the rifle and cartridge later.
*The other method I've read of is swaging: take a piece of flat steel plate and drill two holes: one for the case body to fit through, the other, slightly larger, for the rim. That one has to be shallow enough that you can put a flat punch on top, whack it, and swage the rim down.
**I've used this lube on many different bullets for rifle and pistol, and it works quite well.