Tommys229, I was not aware of that history with either the .40 or the 10mm. Cool to know
My brother has a SIG 220 in .40S&W and I love shooting it. Great round, hit what I point the thing at, but so does every 9mm or .45 I've shot, with comparable results. Ballistically, they're each a tradeoff. (Assuming 9mm +P) I - unfortunately - have only heard stories of the formidable 10mm, so I can't speak to it. Maybe one day.
I concur, also, that if the boys need a little something, if they really need it, they should have it. (Regardless of what my thread is about) But, to me, 6.8 is so new, cannibalizing a 7.62x39 might be easier for folks like me in public affairs who have to explain stuff! (Meaning: we won't have to.) To me, that trade-off would not resound well in a public forum.
To credit you, Tommy, being as I'm a former tanker, I've always looked at a 5.56 and was baffled as to why the .308 was ditched, period.