I gotta agree there should be at least a listing of US headstamps tacked on this forum.
RA = Remington Arms
WCC = Winchester Cartridge Company
LC = Lake City Army Ammunition Plant
TW = Twin Cities Army Ammunition Plant
TZZ = IMI loading for US contracts (I don't know if I ever knew what it stood for)
There are others that are less common today but were very common in the past, such as Dominion (a loading plant in Ontario,Canada that produced tons of M2 Ball) and ECC (Evanston Army Ammuntion Plant, IIRC, which produced a lot of steel cased ammo; I have most of a box of empty ECC steel .45ACP cases in my collection).