Even "fielded" is tenuous, at best (though
I'm waiting for H2O's answer with baited breath): I was attached to the 45th Infantry Brigade in Afghanistan. We had a Connex full of M14s that we didn't use. They might have shown up as "fielded", but we used almost none of them...no point. Of course, this might be H2O's supposed "Vietnam" rifles that shouldn't be considered, anyway.
The (two different teams of) ODA I was attached to had M14s, too. They never used them. No point. Even the grizzled 18B I talked to at length about it told me he mostly played with his accurized M14 as a historical curiosity. (I don't think I saw him pull it out in the two months I was around him.) He said he much preferred the Knight. I saw shorty and full-sized M4s, MP-5s, two Barretts, MK 19 and 47s, M249, M240s, M2s, several different types of shotguns (including one Serbu), M16s, Carl Gustaf, M136s, and three different types of mortars used in Afghanistan by U.S. troops. I think I saw two M14s carried my entire time (10.5 mos) there.
It might be especially germane to repeat that I was attached for several months to troops who had access to virtually any weapon in inventory.
I never saw them use an M14. Not once. The couple of times I did see M14s, they were carried by regular troops, and did not have optics.
John