1. Look for extractor marks and maybe the ejector marks will be
present.
Offcourse you should look for all any other marks.
2. You may have a small chance if the ammunition is special. I.e, if it
is made in small batches. In that case try to get information from
the manufacturer about numbers, how many machines involved in
the production and any thing which will help you to determine how
much is that ammunition unique.