It is 8X57. My gun has a checkered past. It was made in the U.S. for WWII in 30-06. From it's markings it went to Israel, which at one time had standardized on 8mm for small arms, due to the masses of guns recieved in '49 - '50 that were ex-Nazi guns. They later changed to 7.62 NATO when they adopted the FN FAL. My 06 and 7.62 barrels are US, the 8mm barrel is Israeli marked.
And yes, 8mm feeds well from the cloth belts, I have not tried it in links (06 and 7.62 links are different).
When I was in Israel in 1971, (Teaching for the Gov.), we got to an outpost in the Golan Heights. They had small arms in 30-06, 7.62 NATO, 5.56, 7.62X39, 7.62X54R, 9mm, and a Russian Made 1/2 track. Supply must have been one heck of a problem.