Are you sure the compliance with the Buy American Act comment?
I get your point, and it does highlight the issue about "Made In America." It's not easy to find out factual information on it, when some of the 1911 crowd discovered their US marked pistols were actually coming here already rollmarked - from a foreign country - it wasn't pretty.
We don't really know what SIG did. Goes to AR's, too, peruse the Brownell's catalog and you will see they tried to exercise due diligence with AR parts but half the catalog isn't marked with a Made in the USA flag in the corner, including lowers and uppers. Oversight or revelation comes to mind, however there are AR plants in foreign countries that insist on domestic manufacture for their national security, too. Like that description of the "American" biker - Porsche does the engineering, his boots came from overseas, his jacket Sri Lanka or China, the burger ingredients from Argentina, Guatemala and Mexico.
We claim we are willling to start fighting globalization but the protest signs we use are written on imported pasteboard using imported markers and stapled onto a Canadian growth wooden stick with Brazilian metal staples.
On the OP's post, we are missing a valuable resource for selection - why is the focus automatically a NEW gun every time? You want known US made goods, buy used guns. It is interesting to note, tho, that the OP wants a truly 100% American made gun - in a German cartridge. Nobody has pointed that out yet.
I have a 100% US made gun in a US designed cartridge - a S&W 4566 TSW. Excluding the bulk of US makers and then choosing a foreign designed cartridge doesn't seem consistent if the goal is made in the USA. BTW, S&W was known to be hobbing the gears for HD transmissions - there are very few manufacturers who do everything 100% in house. Because of that you never know if one lot or another has foreign materials in it. Even Colt has their AR forgings done by others.