I just ran the measurements and it looks like the chamber could be recut to 8x57JRS. The barrel is about .323 so the .324 bullets should go through without a problem. The proof marks on the gun are close enough that I'm not certain it would even "knock it out of proof". The era of the gun was correct for 8x57. The measurements of the barrel are right to accept 8x57. Guns like this most commonly had 8x57. And the only proof I have right now on the gun that alludes to cartridge beyond 8mm is a 58, which could easily have been the chamber length of an 8x57 JRS.
I think it should be left as original unless the bore is spent, which may lead to a reline, etc. If the bore is rough, jacketed bullets might bridge the gap. 8x58 Sauer(or 8x58 Collath) is what the chamber is and is an interesting round. Fresh ammo may not be available but you could either use 360 BPE or maybe even 38-55 and convert it to 8x58 Sauer.
To answer one of your previous questions, the longarm was made in the Zella Sankt Blasii/Mehlis region and proofed at the Zella-Mehlis proofhouse.
Kind Regards,
Raimey
rse
