Originally Posted by muffin
Can someone explain why there was a need for a reamer/mandrel/Boolit/Bbl-bore with a diameter .007 less than one already on the shelf?

What does that -.007 'DO' ?

Wondered that myself. Came across one explanation (forget where) that said when Winchester was developing the new cartridge they figured Americans were still a little sensitive about getting shot at by "European" 7 and 8 mm stuff so they made sure to develop a new non-metric caliber.
Don't know if true, but its a story.