So far, the count is up to 32 calibers, counting a couple of rumored calibers. Here is the revised list:
5.6x57 RWS
.243 Win, .244 Rem
.257 Rob., .257 Wby
.264 Win
6.5x54 MS, 6.5x55, 6.5x67, 6.5x68S
6.8x57 Chinese
.270 Win
.280 Rem
7x57, 7x64
.308 Win
.30-06, AKA 7.62x63
8x56 MS, 8x57JS, 8x60S, 8x64S, 8x68S
9x56 MS
.338 Win
.358 Win
9.3x57 (Rumored)
9.3x62
9.5x56, AKA 9.5x57
10.75x57 (Rumored)
10.75x68
.400/.375 H&H
.458 Win

Any others?