I have the same problem. I am using Lee reloading dies. I removed the expander from my 243 decapper/sizer die and and measured the widest part of the expander. It only measured .234". That means the brass is about .233 inside diameter. That's much too small, isn't it? How big should that expander ball be?
I've noticed the same problem with my 300 WSM
loads - they always shave a bit of copper off the bullet. I have Lee and RCBS dies for the 300. I guess I'll measure both of them.
When I reassemble them, is there a trick or something to get the decapper/expander exactly in the middle of the die?