I recently acquired this German (i believe) rifle with 6,3mm over 52 marked on the bottom of the barrel. It also says KmG with a line under it and 75gr below the line. It has the crown over B, crown over G and crown over U as well. Just below the 6,3mm over 52 are the numbers 1037 over 331 with a sideways 4 under that. Can someone help identify what caliber it is as I would love to be able to shoot it. Thanks for all of your help!!

Scott