I have a Forster Bushing bump neck die 300WM. I like the thing. Measuring as best I can, seems my inside and outside diameters are fairly consistent after sizing. Just ran a quick comparison today. Pulled my expander ball on my, soon to be history, RCBS Full sizer in 270. ( Maybe apples to oranges)
Sized numbers ranged in 3 -5 thousands difference measuring 6 Norma cases inside and out after sizing. These cases have only been fired twice. I did not compare using the expander. My Forster on Hornady cases measured much more consistent after sizing. It's set to push shoulders .002. I know my test isn't rocket science but enough for me to get rid of expander die on the 270. Just hate it when the expander gets sticky and I have to try and lift the bench.