Longwalker
AH elite
Nice drilling! I had a very similar Sauer drilling, same 16x16(65mm)/8x57JR configuration. I shot Gamebore 16 ga. traditional upland 65mm and RWS 8x57JS ammo in it.
However, mine had a little plunger built in to the rifle extractor in addition to the regular extractor. ( can't see your pictures well enough to know if yours is so equipped) I found that I could shoot regular "rimless" American (SAAMI) 8mm Mauser cartridges in it with no sign of excess pressure and no problem extracting. "8MM Mauser" as loaded by Remington and Federal etc. is a kinda low pressure in-between loading with a light 170 grain bullet that is in between the two correct CIP 8mm diameters. The loading is designed to be safely used in old smaller bore 8mm's without too much pressure.
I preferred the much more powerful RWS loading of 198 grain bullet at about 2400 fps, but you may find the regular 8mm Mauser loads work OK in your gun.
However, mine had a little plunger built in to the rifle extractor in addition to the regular extractor. ( can't see your pictures well enough to know if yours is so equipped) I found that I could shoot regular "rimless" American (SAAMI) 8mm Mauser cartridges in it with no sign of excess pressure and no problem extracting. "8MM Mauser" as loaded by Remington and Federal etc. is a kinda low pressure in-between loading with a light 170 grain bullet that is in between the two correct CIP 8mm diameters. The loading is designed to be safely used in old smaller bore 8mm's without too much pressure.
I preferred the much more powerful RWS loading of 198 grain bullet at about 2400 fps, but you may find the regular 8mm Mauser loads work OK in your gun.