Reeferman:
Disclaimer: When I made this there was no commercial kinetic pullers. I believe this design (certainly not mine) gave companies the idea. At the going rate of modern commercial plastic varieties, there is no monetary advantage, especially counting the time and effort to build it. Its only advantage is that it might last a lot longer.
I don't have any control over how safe you make yours.......the case head, absolutely, must be immovably centered in the case holder to prevent a primer from hitting any metal on said case holder, which might detonate the primer.
Such an accident has "supposedly" happened when owners of plastic commercial tools substituted reloading press case holders for those made explicitly for said plastic commercial tools and the experimenters didn't make the case immovable. I say supposedly because I have never seen any photographic evidence that such an accident actually ever happened. Yet, you don't want to be the first....even so.
My pictures didn't make it from Photoshop's fiasco a couple of years ago....the only ones I permanently lost......and I haven't made any more. But I'll try to explain the business end (or where the case holder is):
1" iron cap---has foam in the bottom only for to reduce depth and force the case holder up against the reducer. I made a plastic ring to fit inside the shell holder by wrapping Dymo Embossing tape backwards (adhesive backing removed) around a shell holder until it made a tight fit with shell holder and ring inside the iron cap. It took two or three wraps as I remember.....The ring, not the shell holder was glued in place in the cap. So for example, if you use red tape, the red side is against the shellholder sticky side out then wrapped...each wrap sticking to the one under. That means when you're done the shellholder can drop out....everything else is held fast. Expoxy was applied inside the cap, then the ring...shellholder inserted was set in place.
Screwed together Shell holder rests against the next part, the 1" to 3/4" reducer (rest of tool except the other end is 3/4" pipe and fittings) held tight there by the foam behind the shell holder in the bottom of the cap. All hammer force is applied to shell holder/reducer connection.
The critical part of this is what holds a case in the center of the case holder:
For that I made another ring out of the Dymo Embossing tape (a form)...just a couple of wraps....red side in...and vaseline-coated the inside, the shell holder and a cartridge case. Case was mounted to the case holder, ring surround applied, then a good grade of epoxy putty....with metal strand reinforcing was pushed into the space in front of the case where it would ordinarily slide out. Then cured. That operation was repeated for each caliber, so each shell holder has it's own case retainer.
Once cured the new molded epoxy case retainer can be slid out and all is then cleaned of vaseline.
Result....when the tool is to be used, the cartridge is inserted in the case holder, the epoxy "case retainer" is inserted, and the combination is mounted, cartridge first, onto the iron reducer, cartridge hanging inside. the cap, with it's shell holder profile modification, is slipped over it and screwed on.
There! Simple! Clear as mud, right?!