Texasjack,
The caliber is 8.15x46R(unless rechambered),as shown by the marks 7.6 and 46. The bore diameter(not groove or bullet)of 7.6mm is common in ihis caliber, even though it is very tight. One of mine is so marked and it has a groove diameter of .312". My cousin also has one,his with .3125" grooves.The express type bullets used in factory ammo is .324", but made so as not to elevate the pressure significantly. The case length is shown as 46mm, they didn't mark the "R".The rifle was proofed in the 10th month of 1936 as shown by the 1036.The number under this is the ledger number.As Raimey said, it was proofed in Zella-Mehlis, and they marked ledger numbers, while Suhl didn't.Since you have 8.15 ammo, it won't be necessary to make a chamber cast. Just fire it and the fired case will tell you if it has been rechambered.You should, however, slug the bore to verify the groove diameter.Unless you can find factory type bullets,you should either use jacketed bullets to fit,or cast bullets a couple thousanths over.You may use oversize bullets if they will easily go into a fired/unsized case. I hope this helps.
Mike
