long, reloaders like to be close to the rifling. I have found you will get best accuacy close in some situations. The claim I find to be true is the bullet will ahve less jump out of the case and will wobble less, due to neck tension variations, seating variation, and will hit the rifling much more straight and therefore the bullet will be much less destorted coming out.

So you can use a tool like i have called stoneypoint AOL guage where you take a case and put it in the chamber with the tool, and you push on the bullet until you just feel it hit the lands and grooves. Take it out and measure the COL or ogive if you have a comparitor.

But the poor mans way is taking a sized case and taking a dremel tool and cutting the neck so you can put a bullet into it but with alot of resistence. (Too little resitence and the rifling can grab onto it and pull it out of the case some and false values.) Chamber the round in your bolt gun and carefull remove it. Be careful not the lest the extractor mechanism shove it agaist the action. Not measure the COL fo the bullet/brass combo.

This is handy in my situation where the throat is much shorter than SAAMI specs.

I don't want to be into the rifling. You can get a pressure spike and that will cause pressure signs before you reach your full potiential velocity.