I don’t normally get 20mm rounds, but this one caught me as something uncommon. The projectile shape and internal case construction seemed odd and interesting to me. Any ID help or comments appreciated.
The projo and case are polished steel, with a copper driving band. There appears to be a steel pin through the case, approximately an inch from the base, that secures an internal weight that does rattle a bit. Other than the headstamp, the only markings are on the projo: