To copy/paste from the CB thread:
Actually... take your spring loaded idea and instead have:
|B|--- --|?|SSSS|B|===
Where B = a metal bar, --- is a tack / nail / etc, S is a compression spring, and ? is some way of attaching the spring loaded nail/thumbtack/whatever to the spring, === being the bit of the spring guide rod that free floats out the other end.
If your guide rod is |===== shaped, a small folded over bit of metal in a C shape would possibly do.
This would get you to tack/nail points to press against the tip and nose of the boolit with a quick release mechanism for sanity.
Would have to make sure the tack/nail/brad you use is of decent length so that it doesn't shadow / interfere with the PC application.
I'll hit hardware store and eyeball this. Springs through local sources can be difficult to be had at 'sane' costs (we are talking 50-200 springs).... but can be had online at better prices. Barring a spring, if the bar is tapped, a bolt with an easy-enough-to-grip head would be a valid alternative (welding wingnuts sounds applicable)... you should only need 1-2 revolutions to apply enough force on the pins.
Sheet metal / whatever base, has tacks / nails on 1 inch centers.
Bars are held above it that have either a spring loaded contraption or just a threaded holes that push another nail / tack downward.
Thus, you have a bullet nose and base being held in place via a couple 'needles'.
Make the bottom nails long enough enough that the PC gets under it just fine...
As far as 'easy to grip bolt head' -- i'd venture a wingnut between two other nuts would work as something to manipulate with fingers ?
A fun question with something that's threaded like that... how does powder coat in the threads affect stuff ?