You got me thinking so I went and measured my C&H .44 mag dies. .4495 on the ID of the carbide sizing die. I rotated the die arouind the calipers to check roundness also. Right on.
I then ran 12ea mixed brands of Special and Magnum cases thru that die. All of them measured exactly .4495 when done . I don't know how many times each of these cases had been fired but I'm pretty sure it was more than once.
All measured exactly the same and there was no variation between the spec and mag cases. Which I would expect since they were pushed thru the same hole.
I don't know what you guys are doing to get these results? They make no sense.
The only thing I can suspect is that your calipers inside and outside measuring surfaces are not calibrated together. A .001 difference in the OD and ID surfaces would generate a .002 difference in OD and ID measurements. Also a .001 diference on a set of chinese calipers would not be unusual at all. I have seen much more expensive tools that had as much or more discrepancy. I used 2 sets of 12" Mitutoyo calipers and a 6" set of Tesa brand (Swiss) and I can calibrate them with ring gauges of known sizes and Jo-blocs which are exact. I use them in my machine shop every day.
Also when taking an inside measurement you must hold pressure on the calipers and rotate the item until you get the calipers exactly square to the measured surface. The reading will stabilize while you are rotating the part. You will end up with the highest measurement you can repeat.
Same holds true on OD measurements on a round piece. UNless the calipers are perfectly square to the piece you will get bogus measurements. You also want to avoid the ends of the caliper jaws as the jaws flex to some degree, measure in closer to the middle of the jaws. On OD measurements you take the lowest measurement you can repeat. Just clamping the calipers onto a piece one time is not a valid test. You must get the same reading several times to confirm that you got a good one.
Also on an OD measurement on a round piece you need to rotate the piece to check for roundness. This would be especially true of a brass case as it would be very easy for it to be out of round and measure a few thou either way when readings are taken at 90 degrees to each other. You could then average the two readings and come up with the actual diameter.
It took me several years to be able to take accurate measurements with dial calipers, and I scraped a lot of parts due to bogus reading of my instruments. I finally learned that I needed to take the same measurement several times to make sure what I got was what was actually there.
This is my only explaination for what is happening with your guys springing brass. I cannot make it spring in my shop.
Randy