Lancaster,
You are right, seems these calibers were “free” until 1956.
Like you I have heard about 7x57 MAS rifles and I remind, when I was a boy (a long time ago…) dreaming on a catalog from MAS with pictures of the MAS36 commercial versions offered in 7x57, 8x60S and 10,75x68.

DORLEAC
www.dorleac-dorleac.com