All of the sizing in the Collet die takes place at the very end of the stroke, when the ram/shell holder appears to bottom out against the base of the die. If you lean into the handle at this point, you will force the collet up into the die body, and cause the collet to squeeze the case neck down against the mandrel (the very end of which pops out the spent primer). About 25 lbs. of force is sufficient to resize most cases. If you are sitting in front of your press, just leaning your upper body weight into the lever is about right.
A good way to determine how much is necessary is to start the case into the die and feel the die remove the primer. Start using pressure and work up to what you think is about 25 lbs. Remove the case from the die and attempt to place the intended bullet in the case neck. If there is little or no resistance, repeat the process with slightly more pressure. When you have reached a point where there are vertical striation marks on the outside of the case neck or the intended bullet does not fit easily into the case neck, the correct amount of pressure has been achieved.
