onondaga
posted this
25 February 2013
http://www.castbulletassoc.org/view_user.php?id=2607>biddulph:
Backjacking is just backing the die off from the correct per instructions setting of the Lee Collet Neck Sizing. This works easily with a Lee Press that doesn't toggle over and is a very linear setting with a Lee press.
The setting for normal neck sizing with the collet die is one full turn in past first contact of the collet with the shell holder. That one full turn moves the die 1/14” inch and allows full closure of the collet to squeeze the case against the mandrel inside the die for neck sizing.
The Die can be adjusted less than the full 1/14” for less squeeze of the collet to accommodate larger diameter cast bullets.....that is “Backjacking” a Lee Collet Neck Sizing Die.
You can micrometer measure the outside diameter of the case neck after sizing to verify the gain in internal diameter of the necks for cast bullets and easily see the difference as you adjust the die in small increments. It is a sensitive adjustment and consistent press operating lever strength is necessary. I always use 25-35 lbs lever operating pressure regardless of the collet setting.
This has to be done backwards to make any sense because every time you adjust the die out for less collet squeeze you would have to use a new fire formed case for a valid measurement. But if the die is backjacked first , then you can do the adjustments in with 1/8 increments using only one case until you get the neck tension on your bullets that you desire.
So, when I know first that I have oversize bullets, My initial setting with the collet die is to just contact the shell holder then I adjust the die down in 1/8 turn increments and I check the bullet tension every time I adjust till I get what I want.
I hope I have not confused you.
Gary
