I'm not sure I'm following this correctly--do you mean it's too risky to size a case that has a live primer?--Ummm yes, obviously, but I think the idea is to remove all existing residue from a spent case and then size before repriming. If you mean it's unsafe to use a press to seat a bullet in a charged case with primer--how is that less safe than doing it by hand--in which case the difference I see is the hand held die goes grenade while you're holding it as opposed to having it held in the press?
If I am understanding it correctly, the OP is talking about reloading .22LR cases, and using the regular centerfire cartridge reloading tools (press, shellholder, etc) for at least some of the work. I see a potential problem with that.
Now, there's no problem resizing the fired brass by holding on to the rim, (obviously) but once you've done that, you're putting fresh primer compound into the rim, (making it "live" again) then powder in the case and the bullet.
Seating the bullet (and possibly crimping) I don't see as a high risk, even with the live rimfire rim, because the force pushing the case into the seater die is applied to the entire bottom of the case, NOT JUST the rim where the live primer now is.
Where I see a potential problem is when its time to remove the now assembled round from the seater die. When everything works normally, it takes amost no "pull" to remove the now loaded round from the seater die, Sometimes they will just fall free of their own weight.
But, what happens if things don't work normally (for any reason) and the round sticks in the seater? Using the regular style centerfire shell holder, with its slot holding the case rim, means lowering the ram puts pressure DIRECTLY ON THE PRIMER inside the case rim. What if its enough to crush or tear the rim?? That could result in detonation.
I know its hugely unlikely, but people do win the lottery (both the good way and the bad way), so I think using a different approach for that part of the reloading process, a way that puts no pressure on the rim, in any direction, would be a better idea.
Didn’t the Lee loader require you to hammer the primer in .
No, it did not. Though it may seem to look that way, that's not how it worked. You used the hammer (or a bench vice) to apply force on the tool which pushed the case down over the primer, seating it. ALL the force was applied to the case, no force was applied to the primer. The primer was not "hammered" in any way whatsoever.
This is also the way a press mounted priming arm primes cases. The primer is held stationary (no force is applied to the primer) and the ram pulls the case down over the primer, seating it.
My suggestion to eliminate the admittedly small risk of applying force to the primed rimfire rim would be to use a system without the regular centerfire shellholder slot when seating the bullet.
A push against the entire base of the case evenly should be fine for seating and having the die set up to allow the use of a "knock out rod", if needed would, as far as I can see eliminate the risk of putting pressure on the live primer rim.
I think taking the regular shellholder design and cutting it off flat, removing the hook part that forms the slot, and leaving just smooth platform would be best. It can push up, but without the hook part cannot pull down. Evenly applied pressure against the entire base of a rimfire round is fairly safe, pressure against only the rim (in either direction) is not.
I would also make sure your seater die has a clearance cut in the bottom to make certain there is no possibility of crushing the rim between the die and the shellholder.
Its tougher to explain than to illustrate, but drawing on the computer is beyond my personal tech skills. Sorry...
