Once upon a time, there was a lot of milsurp Egyptian 8x57 ammo at gunshows, etc.  That stuff was very high powered.  It was packed in 50-round boxes, no stripper clips.  Maybe for MGs, but it certainly made its way into FN 49s.

I think the early 8mm rifles you refer to are the pre-1904 Model 98s made in Germany.