I hope I can help here.
First, that R * 2 * 46 * headstamp is Brazilian, used by the Realongo factory, and it is commonly found on 7x57 Mauser rounds. I would check the length of the rounds. It has also been used on Brazilian .30-06 production, so it might be cases that were later cut down by a .308 reloader. There absolutely was no .308 Win. production in 1946.
As to headstamps, I think I'm on pretty safe ground stating that there is no "secret" headstamp or marking guide available to law enforcement only. CSI-type guys are always asking cartridge collectors for headstamp info, and we actually have a good number of them in the collecting fraternity.