Originally Posted by iskatel
I want to describe the problem graphically!
.... for the prevention, understanding errors.
The term here to use is case neck run out. The key word would be run out.
Definition "Run Out"-To occupy or exist in a certain range. ie: The size, or in your case,"thickness", runs from small to large.
Are you using a ball micrometer to measure this thickness variaton of the wall of your cases? Or are you using a case neck guage to measure this variation in wall thickness? Also have you chamfered the mouth of the case before making your measurements?
A vernier caliper is not the tool to do this with. Also a ball micrometer is difficult to get consistant accurate readings without practiced use of them. A case neck guage would be the way to go to make this measurement. In your situation (pistol ammo) I dont think this variation is critical.
Case neck run out over .0015 to .002" in bottle neck cartridges (rifle types) will affect accuracy, which stalking bear said could be cured by neck turning, however, I dont think this holds true for pistol ammo.
One of the better seasoned reloaders on this forum hopefully will chime in soon and address this problem of your 9mm pistol ammo run out situation, which I dont think is a problem.
I measure neck run out on my bottle neck rifle ammo and will turn the necks to correct if the run out exceedes .0015". When it comes to my rifle ammo, however, I'm a anal retentive arse. I also have lately begun reloading .44 mag for my pistol and for ****s and grins measure run out on a few of these cases with a ball micrometer and there is some run out variation from time to time which I pretty much ignore and reload.