Depending on who you believe, the body diameter just forward of the rim is either 0.476" or 0.471"

Norma used to do the brass and loaded ammo.

I understand that Privi Partizan in Serbia are making it these days, though not in huge runs.

Chambers can be a "little" larger in diameter than one would expect. Late war ones are sometimes "agricultural" to say the least, but they work. Just don't expect a lot reloads from your brass.

Any good .311 / .312 bullet of about that weight will do. Power-wise, it is pretty much on a par with .303.

Thus, loading data for .303 is a good place to start. Original bullet is , I recall, about 184gn.