I have an odd two piece projectile. The length is approximately 46.7 mm. The dia just above the grooved cannelure is approximately 13mm. It is approximately 12.7mm on the grooved cannelure. The body section takes a magnetic and appears to have been drilled out. The nose screws into the body counter clockwise and is non-magnetic. See photos which show all views and comparison to .50 cal bmg ball round.