You could make a case for the M1/M14 Garand in some ways (and maybe the FN-49) from a production standpoint. These are the last mass-issue rifles I know of that were built to the "old world" standard.
The M1/FN-49 were heavy, built to last generations, and very expensive to produce. The AR is lightly built, expendable, and cheap to produce. Even the AK, while not "lightly built," was a modern weapon from the perspective of mass production, and was intended to be expendable.
Rifles like the FAL/G3 were also much more modern weapons from a production standpoint than the M1.