1 in 8.66" is the original 19th century rifling pitch for the 7X57 in the M1893 Spanish Mauser and was copied (why not? - it worked) in most if not all military 7X57s into the 20th century.
When the first US manufacturer produced a sporting rifle later (Remington?), 9" was used and I think most American commercial longarms have used this since, although SAAMI lists the standard rate as 1 in 8.75". For some reason, Remington went a bit slower with the 7mm-08 (maybe because it could see that 140-150gn bullets would likely be the heaviest used in commercial ammo) and SAAMI lists it at 9.5".
