Subject to seeing any proofs on the barrel flats, there is a better than even chance that it was lined in the US. Had it been done in Germany, it should carry a "repair" proof, and new caliber designation, etc. I believe a chamber cast is warranted; failing that, you could at least fire a 8.15x46R and see what the case looks like. In my mind, the MM on the barrel is why I'm not certain it was lined in the US. That is the mark of Max Moeller of Zella-Mehlis, as opined by Raimey and Suhl makers(Sauer) didn't normally use their products. (However retailers often used them.) If an 8.15x46R case fired in the rifle keeps the correct shape, I can agree it is German work, because an American would have used an available caliber.
Mike

Last edited by Der Ami; 02/07/18 11:20 AM.