I've got some 8 X 56R that shoots in a Steyr Model 95 Mannlicher. It is Nazi headstamped with the year 1936.

I've never had a misfire, hangfire, squib, or any other performance problem.

It came packaged in double layer cardboard boxes already in the loading clips.

So, to answer your question, .. if stored correctly my experience is that shelf life is at least 74 years!