Shoulder bump/set back not bumping but growing

[Icefire]

So I bought a Cadex in 6.5CM and some new Peterson SRP brass for it.

They were first fired with either 90gr or 147gr bullet, not jammed at 85% published max load mostly to get them fireformed.

I just setup some new die (Redding Match S FL with 290 bushing) and proceed to try to get max .001 set back. I zero’d my caliper on a case with a 30 cal buller comparator (Hornady) and sized than checked, screw the die more, size again, check again.

Now I’m nearly touching the shellplate and the case shoulder is slightly advancing and not backing off?

It grew +.002 now it’s +.001 with 2/3 of the neck sized.

On my 300 Winmag, with 1/2 the neck sized I’m at -.0005?

 

[bigedp51]

Chambers and dies vary in size so nothing is written in stone about die adjustment.

My guess is the dies shoulder has not started to push the case shoulder back to your desired amount of shoulder bump.

In the process of sizing and squeezing the case diameter the shoulder is squeezed upward and actually becomes longer than the chamber.

Below your die is just above the red dotted line and the die is not adjusted down far enough to push the shoulder to your desired amount of bump below the red dotted line.

Just keep adjusting the die downward very little at a time until the shoulder is bumped to the desired amount "below" the red dotted line.

Right now you are at the point where you want to test fit the case in the chamber and fine tune the dies adjustment downward.

Remember the brass springs back after firing so the case shoulder is very close or just under actual chamber headspace right now.

 

[John Y Cannuck]

If after reading the above you decide you still need more set back, you can modify or replace the shell holder to get a thinner one.
They are not all the same. If for example you compare a Lee with a Lyman, chances are you will find different dimensions. I had a battle with a tight chambered 308 that turned out to be an out of spec shell holder , not the rifle at all. Brand was unknown, got at gun show.

 

[Icefire]

I was sugested it might be the expender ball that I did leave there in the 6.5 and not the 300 WM.

I’ll try tonight and also check neck runout.

 

[Quiet]

I have had this happen with very soft brass where the expander ball pulls the neck and shoulder out on the down stroke.

 

[Icefire]

I did 150 case tonight as it was setup, .0015-.002 outside neck runout

I guess the expender ball was pulling on the .290 resized neck