Just use a cut off 22/250 sizing die,trim to length and turn necks and fireform
Not original with me, but if you'll trim the cases first and then run them through the cut off .22-250 die without an expander in the die, you can set up the die to where the bolt will just close on the case. My chamber is a .246" neck so the cases will chamber before you neck turn as long as you haven't run an expander into the cases. After moving the shoulder back with the shortened .22-250 die, neck turn and fireform and you're done. I also use an extended shell holder with the .22-250 die where I can lock the lock ring and have it set for the next time I want to make cases.
For me the main problem for making .22 PPC .100 short cases has always been trimming the cases to length. If you trim off about .085" off of them first, you can do it with a Wilson case trimmer with a .220 Russian case holder and a power adapter that will let you use a cordless drill. The power adapter is available from Wilson. The .220 Russian case holder will hold the case tight so is simple to run the drill as fast as you want to remove the excess neck length. I hold the case trimmer in a table mounted vise. Trimming to length with power makes short work of trimming cases to length. Make sure and oil the cutter where it runs in the case trimmer or you can gall the spindle. You'll still want to check case length after you fireform and cut them all to uniform length after they've been fired a couple of times.
1. Trim off .085" off first on all the cases in your batch.
2. Move shoulders back creating the fireforming shoulder.
3. Expand the necks on all the cases to match your neck turner mandrel.
4. Neck turn all the cases.
5. Fireform as many case as you want to fireform.
6. Reload the cases and fire them a second time.
7. Trim to match your chamber length. I go .020" under the chamber length and use .010" under chamber length as a maximum case length.
8. If I happen to have a doughnut, I'll take it out with a .224" chucking reamer.
That's how I did it the last time I made cases for a .22 PPC .100 Short. I was using a Harrel die and was having a little trouble with my cases getting tight as the die wasn't sizing enough. I sent some cases that had been fired through a match to Jim Carstensen and had a full length bushing die made to match my fired cases. I haven't taken it back to the range since getting the new die, but I'm sure that it will solve the tight case problem.
As with everything in benchrest, there's more than one way to do just about anything. This is the easiest way I've been able to make shortened PPC cases.