Mike, I'll post some photos of the markings on my MS once back home as I am currently travelling, in the meantime you may already have a look at that old post as it also includes some info about late XIX / early XX centuries Austrian rifles bearing only British proof marks
http://forums.nitroexpress.com/showflat....true#Post289862
Another option, not yet discussed, may be that Steyr sold at that time unproofed barrelled actions to some British rifle makers?
Louis