A large amount of Portuguese .303 was also made with a big pocket, and a huge anvil that had a groove formed across it and a single, small, central flash-hole. This stuff had BRASS primer cups (at least the stuff I've seen), thus it will be a LEAD based primer, not the case-rotting mercuric model. However, I believe the primer diameter is .256" and thus the same size as in a lot of other European ammo, RWS used to sell them, but that was a while ago.

See pic. in this old post: http://www.milsurps.com/showthread.php?t=33847