At NRA Matches only...
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
Will there be a "What the captain means is..." message from NRA? Probably.
In the meantime, will firing lines be flooded with rifles mounting red dots, ACOGs, etc? Probably not.
If you can't do everything else necessary to break a 10 will an optical sight put you in the winner's circle? Definitely not.
But it isn't likely the rule change will be completely undone either, so if that's what you want to do it's OK under the rules now.
Maury