links with holes were the standard when I was in, back in the 70s. Can't tell you what the official standard is today, or even if there is one. But I can tell you that its highly likely whichever one is in inventory is the one that will be used.
And by that I mean that as long as the ammo is considered servicable, it will be issued for use, holes or no holes. We were fed the "last" of the Korean war era C rations in the mid 1970s. They were still "servicable" (officially) and were issued, and ...eaten. In fact, most of us actually preferred them to the new "Vietnam" era C-rats...the older ones had smokes in them!
