Because of the rotating block, and because the top of the block scribes a larger arc than the center of the block, it is difficult to head space off the shoulder in a Martini. At minimum the top of the breech block will drag across the head of the cartridge when the breech block is closed, at worse the block won't close.

SAAMI specs are for guns other than Martini, a greater gap is need for the rotating block thus the .010 figure.