I'm glad you actually linked info, that may be an older document, if you look in the munitions list it excludes or rather says USCBP and post shall permit them.
I have talked to Prophet River, good fellas, purchased a few things from them. havent chatted lately.
There is a scope at home in the safe now (below) that you can argue with in person that it is not possible and prohibited for it to be here if you want.
[url=https://flic.kr/p/2hsFBJb]
Stock is in progress. There was a USCBP or something paper in the box with it. I tossed it, it had both their and DHL's info on it so it did go through inspection/review.