I believe we may be being deceived as to the scope of application.
If you Google US Munitions List, you should be directed to a link. 22 CFR 121.1 which details what is covered. At the end of paras a thru i is a Note
"Note . This coverage by the US Munitions List in paragraphs (a) through (i) excludes any non combat shotgun with a barrel length
of 18" or longer............
Thus working on sporting shotguns is fine,does not require ITAR registration, we may continue to drill and tap for mid beads and remain felony free.
The note specifically goes on to state "This category does not cover Riflescopes and sighting devices that are not manufactured to military specifications."
So adding a commercial scope to a gun, including drill and tap as required is not an ITAR covered activity.

What may well be problematic and subject to government overreach would be whether this can be applied to working on AR15 type Rifles. I would be most interested on what the ACGG's Legal Counsel have to say about it's scope and implementation

Hugh Lomas,
H.G.Lomas Gunmakers Inc.
920 876 3745