Thanks to an overseas collector and IAA Member, I was able to acquire this beautiful inert, Russian, 100mm BM20 APFSDS-T projectile. Last week, I was fortunate to purchase a Russian, brass 100mm case (also from an IAA Member - Bruce) that I hope is the correct match for this projectile fitted with a non-matching primer assembly. The case was captured by Israel and at some point re-marked with hebrew stenciling. Upon careful examination, I observed that there looks to be internal threads on the inside of the case mouth, stopping at the case neck/shoulder. Does anyone have any ideas about this? The treads are VERY shallow so maybe they serve as an increased friction point to help keep the projectile seated??? Totally made that up. I am pretty sure this case was originally fitted with a different 100mm projectile and not an APFSDS-T projo. Anyhow, any ideas on these threads would be appreciated.