Hands down the best round I found at SLICS was this .30 Light Rifle (7.62 x 49) with Bernstein type projectile. The case is FAT 1E1 case and the bullet was designated the FAT 12. The headstamp is F A 49, the primer is nickel plated and has a red ps. See HWS3 p. 159.
Another welcomed find was this 14.5mm from the first year of production. The headstamp is 3B 40. What is neat about this round is that it has a very thick case web.
This next one is outside my knowledge/interest, but it’s kind of neat. I’m assuming that it’s a gas cartridge. It utilizes a shotgun shell primer for the rim and the ‘headstamp’ is on the front face of the case.