Hi!!You have pulled a god one on me. I do not have this one in Vol III. (which is 2 years late due to many problems.) The R numbers do appear in early 1960's for the HV tests preceeding the Vigilante series and would be in Vol IV. Did the case come with the projectile? With the split projectile, it looks like the U.S. made Copies of the German HV types during WW II, but not with a 1953 date. and it would have a Tungston steel core, and a ballistic cap. There were a series of 37mm CBR cargo projectile tests in the 1950's with 2 part aluminum/ steel projectiles and glass packing. The U.S. projectile types for the 37 AT gun went up to M1000. I have samples of 3 diff US Proofs and none are multiple parts but the 37 mm size was useful for ballistic testing of scale model 105/120mm HV tank gun rounds at Aberdeen proving grounds, and so there were a lot of small quantity strange shapes made.