Ok, I think there is some confusion here so I'm going to dummy this up in hopes of understanding this and for the sake of everyone else too.

The old guy, Steve, was using a tool that the case mouth fits into and has a cutter that cuts the outside of the case so that the thickness of the mouth is uniform all the way around.

He said that what he was doing, (Can't recall what he called it), is the most important reloading measure for accuracy. Though in honesty I think he was assuming I was doing most other things right or mostly right.

So what was he doing?

Is that the most important measure?

Just some background, this guy is a really good shot and has probably $100K in rifles and another $20k in reloading equipment. He used to shoot with guys like Sinclair and other big names. He actually just refers to them by their first names.

Tom