Slamfire, kudos and other accolades for your posts on sizing stuff.
And also two attaboys to you for showing the Wilson .308 Win. and reamer cut case gauges. Both made me think of the Wilson chamber type hand seating die I've had for decades. They made me think of another use for any rimless bottleneck case gauge that's reamed to SAAMI or some other chamber spec that lets one see how the mouth fits the front of them.
Take a new or fired case that's been neck or full length sized, then put it in the gauge. Press the case all the way in then look at the case mouth relative to its clearance to the gauge's chamber neck. That shows how well aligned the case is in the "chamber" when it's smacked by the firing pin. If you use an 8X or 10X loupe to magnify it, it helps. A loupe with a measuring scale in thousandths will show how uniform the space is around the case mouth. This shows how well your loaded rounds will fit the chamber when they're fired. It also shows, if you gently push the case in with both held horizonatlly, how the case rests in the bottom of the chamber until it's all the way in when the case neck/mouth centers in the chamber neck/mouth. And moving the back end of the case around doesn't significantly change the case neck's position in the chamber.
All of which may help folks understand why full length sizing fired rimless bottleneck cases shoot so darned accurate.
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Long Range High Master
NRA Smallbore Prone Master