I would imagine that by the time of the M85 it would have been the plastic 'tin'. This was the 'tin' generally on issue at the time/era and was certainly the kit issued with the old L81 Cadet P-H rifles. I could be wrong of course as we only ever saw the L81's (ugh.....) but in the real world, while there would have been a norm, they'd have supplied whatever the purchasers demanded