Hi John,
The 8x60S was 328 bore diameter according to the drawings of the case in the other thread. I never slugged the bore as I didn't have any suspicion that it may have been changed at the time. It shot Woodleigh 330 projectiles and Kynock 330 projectiles fine and I was given some 8x56R ammo and told the projectiles were suitable for the 318WR. They measured 329 and even though they were only about 220 grains they shot like stink. I can vaguely remember some of the proof marks and one of the markings was, I thought at the time 8x60.5, which I thought was dimensions. I am now inclined to think it was probably 8x60S.
It came from someone in Melbourne who you and I both know.
Les