Up until about 1943, the Germans made weapons in blocks of 10,000, which each block denoted by a letter suffix. For example, 1 to 9999, 1 to 9999 a, 1 to 9999 b, etc. Your rifle looks like a "v" block. Since it was once a military rifle, but has now been turned into a hunting rifle, it will be difficult to tell you much more as a lot of the original numbers and markings are gone.