As of 1 Jan 2011 an M1, M14, M16, or M110 with "...no restriction as to sights" is now considered a Service Rifle under NRA Rule 3.1(f). The same as an iron-sighted M1, M14, M16 or M110.
https://www.nrahq.org/compete/rules/rul_hpr_11.pdf
100+ years competing with eyes down the drain!