The reason I asked, I have a Mauser actioned rifle with a German made semi-octagonal barrel in caliber 6.5X57. The rifle is fitted with a G&H side mount, so the markings (if any) on the left receiver wall are covered up. The action has an FN type low scope safety, an FN type floor plate release and a bolt handle suitable for low scope mounting (although it does not look exactly like any other FN commercial bolt handle I have seen). No proof marks that I could find. The receiver ring and bridge are not tapped for scope mounts.

The bolt closes with difficulty on a RWS 6.5X57 factory cartridge, but with less difficulty on my hand loads, leading me to believe that the barrel was fitted to the receiver without the benefit of a chanmbering reamer to get the headspace exactly right. It seems to be a very nice outfit, if a bit enigmatic. I will try to post photos later.