Anyone building one of these should take a look at this page:
It seems that there is some bad ammo out there. After looking at several places for 7.62x25 with no luck I went to an out of the way place I know and he had some. So I picked up some and on the way home remembered reading something about the pink paper wrap. Got home, checked it, and the headstamp is 53 not 52, so it should be ok.