I understood the "S" in 6.5x68S stood for "Schuler", the originator of that round.

I was aware the "S" stood for groove diameter of .323" in the 8mm.

My buddy Keith's second barrel for his 6.5x68 had a 9" twist, which allows up to and including pointy 140's and 156/160gr. RN's.

If I were to buy a new bl. in 6.5mm, it would have an 8" twist. My .260 has a 9" rate of twist.

I have a local friend with a Merkel 16bore over 7x65R. The 7x65R will put 3 quick shots with 160gr. TSX under an inch @ 100 meters with the (horridly -to me) huge crosshairs in the Zeiss scope.