I'm forming some .20 Practical brass from .223 Rem Match Lapua brass using a Redding neck sizing bushing die. After sizing down with the .233 bushing and .225 bushing I'm left with a .240"x.035-.040" ring/donut at the base of the neck. I suspect it's a result of low end SAAMI spec FL sized brass and I don't believe it will be an issue. FWIW I don't have the barrel yet so I can't chamber one.

I'm wondering if this is common? and if not should I have the base of the die or the shellholder machined down .04"?

edit:
I ran a couple of fired .223 R-P cases through the sizing die and they didn't have the donut/false shoulder. It appears that the Lapua brass must have the shoulder set back pretty far from the factory or the die's on the high end of SAAMI spec.