Measure a resized neck and a seated bullet dummy. I'll bet your dummy measures the same or just slightly less.
If that's the case your expander ball is oversize.
Ideally the neck length should be at least one caliber and the case mouth should be just shy of chamber length. Repeated firings with "short" brass can damage the mouth of the chamber.
This gizmo will help you determine the chamber length...
Fix it and bed the front at the receiver and about 3 inches in front of it. Make sure it's free floated, straight in the barrel channel and as stress free as possible.
I have one in 30-06 and it is scary accurate. I'd post about it how and why, but no one would believe me if I did.