I recently acquired the projectile below. It is blue with a magnetic screw off nose. The body is hollow and nonmagnetic. I think the round is a Davey Crockett Practice Spotting Round. It is 20mm. The fellow I got it from said he had 3 others, a red, yellow, and black different from this blue round brought back from Germany in the late 1950’s. What are the colors distinguishing? Is the body possibly deleted uranium?