Brass Lengthening in FL Sizing Die

[Doom]

the OP isn’t saying the OAL of case is growing like
some comments are trying to correct for or explain. His shoulder measurement is. So I believe the die isn’t set up properly and isn’t down far enough to push shoulders back like he is wanting. I have seen this before when I initially set up a FL die. They got longer until die was set to contact shoulder and bump them back

"I'm trying to full length resize and bump my shoulder back ~.002", which seems simple enough.
My resizing die is a Redding S series, full length sizer. It has a neck bushing and the mandrel is removed.

After resizing, cases are consistently measuring .004-.005" LONGER than when they started, which seems impossible."

 

[X-Caveman]

What bullet, powder & charge weight did you use on these first 100? I’m in the camp that the brass hasn’t grown to fit your chamber so there’s no reason to bump shoulders yet. This brass is tough.

The most troubling thing I’ve read is that a fired case will hold a bullet well enough to reload without any sizing. What is the neck diameter of your chamber?

 

[savageshooter86]

"I'm trying to full length resize and bump my shoulder back ~.002", which seems simple enough.
My resizing die is a Redding S series, full length sizer. It has a neck bushing and the mandrel is removed.

After resizing, cases are consistently measuring .004-.005" LONGER than when they started, which seems impossible."

“After resizing, cases are consistently measuring .004-.005" LONGER than when they started, which seems impossible.
This is measured on a set of Starrett calipers that I know to be accurate, using a shoulder bump gauge that measures at mid shoulder - not OACL“

Maybe re read it. He says not OACL

 

[Doom]

“After resizing, cases are consistently measuring .004-.005" LONGER than when they started, which seems impossible.
This is measured on a set of Starrett calipers that I know to be accurate, using a shoulder bump gauge that measures at mid shoulder - not OACL“

Maybe re read it. He says not OACL

Well duh! And I don't remember the pictures in the original post. It sounds like the die needs to be adjusted down to bump the shoulder back. Simple. Kinda like you said.

Forgive me, Kemosabe!