Full Length Sizing

[FiveInADime]

Question:

For all of the cases I reload standard RCBS full-length dies do not bump the shoulder when I screw in the die to touch the shell holder at the top of the presses stroke. I have and use Hornady's gauges to measure, along with sooting the shoulder so I can see when it is touched. I then slowly (think 1/32 turn at a time) turn the die in until the shoulder is barely bumped. I usually achieve an aparant 2-3 thou bump.

What am I missing here? Why the need for the taller shell holders?

 

[Bart B.]

Those taller shellholders let the die be locked in place to set fired case shoulders back the same amount, but with a smaller spread in case headspace. There's typically a 2 to 3 thousandths spread in case headspace if the die doesn't stop against the shellholder. That's caused by the amount of lube on the cases as well as how long the die's ram is held at its high point; the press' springback slowly pulls the die down on the case a thousandth or two if the ram's stationary for a while. With one a few thousandths higher, such as a .129" one that's .004" higher than the .125" standard, and it stopping against the bottom of the sizing die, the die's "chamber headspace" is more consistant from case to case. The spread is typically less than .001" with Redding's competition shell holders properly used.

Measure your case headspace across a dozen sized cases and see what the spread is. How much spread can you tolerate?

 

[FiveInADime]

Those taller shellholders let the die be locked in place to set fired case shoulders back the same amount, but with a smaller spread in case headspace. There's typically a 2 to 3 thousandths spread in case headspace if the die doesn't stop against the shellholder. That's caused by the amount of lube on the cases as well as how long the die's ram is held at its high point; the press' springback slowly pulls the die down on the case a thousandth or two if the ram's stationary for a while. With one a few thousandths higher, such as a .129" one that's .004" higher than the .125" standard, and it stopping against the bottom of the sizing die, the die's "chamber headspace" is more consistant from case to case. The spread is typically less than .001" with Redding's competition shell holders properly used.

Measure your case headspace across a dozen sized cases and see what the spread is. How much spread can you tolerate?

Ok, my morning brain wasn't in gear yet. I previously understood the concept but lost it somewhere along the way. So, adjusting shoulder bump with the height of the shell holder in play you can achieve more uniform results.