I had the same experience with some 7x57 loaded by FN around the same time. They could have had a bad batch of primers, or the ammo was improperly stored.

Incidentally, the reason the US kept corrosive primers through WWII was that the then relatively new non-corrosive primers had not been sufficiently tested for long term stability. Requiring GIs to clean their rifles was preferable to having ammo that failed to fire.

Jim