Just an opinion, (based on an idea I got from Charles Huckabe), there is only one sure fire way to size the entire area of the case web.
you take a standard Redding body die, chuck it up true in a lathe, and using a carbide drill or boring bar, you remove the entire shoulder inside the die, leaving just the tapered body portion of the die. Then face the die untill the bevel on the big end is just about gone.
Using a arbor press, you push the case in so the head is flush with the bottom of the die. You then take a punch that will slip into the cases neck and push the case out.
Then you use your standard sizing die to bump the shoulder
Dies that incorporate a shell holder will always have the problem of not getting the entire web sized down.
As I said, I did not come up with this idea. I started doing this a while back and it does a great job. I have taken 6PPC cases that had developed a severe click and got more life from them using this.
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