I recently found these and wonder why would the box label say no waterproofing at mouth? I would not expect to find waterproofing on any new primed empty. Can anyone explain or provide any insights as to what they were used for? Thanks
These cases were used to assemble “perfect” or “reference” cartridges which were to be the standard against which other cartridges being evaluated were measured. Because cartridges undergo so many different tests, especially during development, cases, bullets, primers, propellant, etc. calibration components were provided so reference cartridges used to calibrate test equipment could be individually tailored for a specific test.
Adding to Mel’s reply above here is the link to a previous discussion on calibration components and a couple of photos that are now missing from that discussion-
Brain Great Box with the PP on the label.