With regard to the choice of 6.5x58R S&S for the rifle cartridge, some hunting areas had only "Low"(small) game and there was no to little chance of encountering "High" (large) game. Even though Reh (Roe) deer is a trophy animal it is included under the designation of "Low" game. The 6.5x58R S&S was perfectly capable of cleanly taking Reh deer and was a popular cartridge for the purpose. If Dixon is correct and the cartridge was introduced in 1897, the Drilling would have fallen under the 1891 Proof Law and would have required proof when it was made. This would negate the possibility that an older non proofed gun might have been voluntarily submitted for proof in 1937, as I opined above.
Mike