The state department is the US agency that defines what articles are considered ITAR items and enforces ITAR. I worked foreign military programs and had dealings with ITAR items on almost a daily basis. Go here
https://www.pmddtc.state.gov/regulations_laws/itar.html if you have any doubt who is in charge of ITAR. They are the only agency who can give you the real "skinny" on ITAR, keep in mind most federal agencies are doing good if they can give you correct information about what their agency does much less be able to give advice on the rules and regulations that are the responsibility of other agencies.
The most common response when someone asks a question about what an FFL can or can not do is to contact your local ATF office as they are the only ones who fully understand what the rules and regs are and get it in writing. In the same vein I would recommend those who have questions about ITAR to go to the link I have identified if they have questions about what items are covered by ITAR.
Here is a listing of firearms related ITAR items directly from the State Department web site:
Category I—Firearms, Close Assault Weapons and Combat Shotguns
*(a) Nonautomatic and semi-automatic firearms to caliber .50 inclusive (12.7 mm).
*(b) Fully automatic firearms to .50 caliber inclusive (12.7 mm).
*(c) Firearms or other weapons (e.g. insurgency-counterinsurgency, close assault weapons systems) having a special military application regardless of caliber.
*(d) Combat shotguns. This includes any shotgun with a barrel length less than 18 inches.
*(e) Silencers, mufflers, sound and flash suppressors for the articles in (a) through (d) of this category and their specifically designed, modified or adapted components and parts.
(f) Riflescopes manufactured to military specifications (See category XII(c) for controls on night sighting devices.)
*(g) Barrels, cylinders, receivers (frames) or complete breech mechanisms for the articles in paragraphs (a) through (d) of this category.
(h) Components, parts, accessories and attachments for the articles in paragraphs (a) through (g) of this category.
(h) is a catch all because if you go up to (a) it covers all firearms "Nonautomatic and semi-automatic firearms to caliber .50 inclusive". It seems to indicate that all attachments to firearms are ITAR items, it does not say anything about the military purpose. Basically if they want to stick it to you they can and will. So proceed with caution aware of the issues. You may be able to get away with scopes because they may not be "manufactured to military specifications" but many of the military specifications for riflescopes are met by any quality optic, it does not call out only the reticle because the armed services have used an amazing array of reticles through time.
While working for Lockheed Martin I performed a demonstration of a small drone system for the British Army in Basra Iraq in 2007 and had a temporary export license that covered every piece of equipment I brought in to Iraq. One line item on the temporary export license was a number of lithium-polymer (lipo) rechargeable batteries. Lipo batteries are hazardous so when they showed up on the manifest on the RAF plane leaving Iraq the captain refused to have them on board as cargo.
When the shipment came back into the country the inventory done by the officials showed the lipo batteries were not present, meaning they had been permanently "exported" on a temporary export license. Since I was the person who signed the export license and did the "exporting" I was personally criminally responsible for that illegal export of military hardware. You will say there is nothing militarily sensitive about lipo batteries as they are mainly manufactured outside the US and available by mail order anywhere in the world, that did not matter. Luckily I worked for a large corporation with a large legal team and they were able to get the charges dropped and it was no longer a problem for me.
The most important thing you can remember is the rules are federal so they do not have to make sense.
Given the climate we are in I am sure that the federal agencies are told by our current president to go easy on gun owners as they are just exercising their second amendment rights.
I will shut up on this topic, I have wasted enough of people's time already, I just wanted people to know where to go if you want to get the actual rules and interpretations of what ITAR is and covers.