This denarius of Caracalla is offered to me privately (first coin). But I found on acsearch same denarius from the Naumman auction, whether it's a die match or a cast copy? Thank you.
It's not a cast copy because the flan shapes (and other things) are different. While the coin does look a bit porous, that doesn't necessarily mean it is a modern fake. The reverse of the subject coin is weakly struck but I'm not sure I'd call it "soapy" (which is a description used when the junction of the devices to the fields are not sharp). The reverses are die matches and the obverses are not a match. I suspect the coin in question is authentic. Here's the outline of the Naumann coin overlaid on the coin in question: Also, looking at the letterforms and style, I bet the same hand carved both dies, at least for the legends.
It's very likely authentic because one of the dies (the reverse) is a die-match, whereas the obverses of the coins were struck with different dies. That's not something a forger is likely to do for a coin of (relatively) low value. If you're interested, here are the five examples in the British Museum collection.
