I can only say this. The only repros I am aware of are the limited run made by machinehead2, and those are not cast. I have originals and they are castings. There may be some differences in the casting marks from different mfgs. At least three separate manufacturers made the 1919A6, and it is possible some of the later production (1950s and 60s) was sub contracted. I have yet to see a bipod head with any mfg markings, so I have no way to ID who made what. But I do know that SAK marked their M7 flash hiders, and that Springfield Armory made some flash hiders too, as I have one with their mark. Don't think SA made any complete guns though. Never seen any A6 component with an SG or RIA mark, with the exception of the SG jackets. SAK also marked jackets. Barrels were marked though, by all mfgs. I think these look genuine, but buyer beware as always.