Originally Posted By: Jabey9210
If the shell holder is touching the die firmly what does it matter what position the press is in? To me it seems that once the shellholder hits the bottom of the die, that's as far as you're going to get it to go no matter if the press is at 1/4 stroke or 3/4 stroke? Not arguing just asking!!!
Cuz...
... when you screw the die down to "touch" the shellholder, the press is not being stressed.
When you run a case into an FL die, it is under a lot of force, so the top of the press starts to be pushed up - it "flexes".
When it flexes, the die is no longer touching the shellholder, so the case does not go in the die for the last 4 to 7 thou... so the shoulder does not get pushed back in place. This is important, because when you partially size a case, the shoulder gets pushed forward, and now is too long.
When you partially FL a case, (like 98% of the way) it is worse than when you started - which is why the original poster (Coxa2) could not chamber cases that came out of the rifle, fitting the chamber, with no problems of tightness... they fit the chamber of the rifle when they were extracted, but now they don't.
What happens is, the FL die starts squeezing the body fairly soon and that squeezing causes the case to GROW longer - so now the headspace of the case is longer than the chamber that it was just shot in - and will not go back in.
So when you set up an FL die, you MUST make sure that the die is still in contact when the ram is all the way up, and the press handle is all the way down... even AFTER the press has stretched/flexed.
That is why it is necessary to adjust an FL die so it is screwed past the point that it hits the shell holder.
The easy way to do it is to screw the FL die down to the shell holder when the ram is all the way up. Then let the ram down and screw the die down an additional 1/2 turn. It should hard to finish the ram stroke, even when there is no case in the press - that is called "camming over".
It is not necessary to do with neck sizing dies.