Large Roman Silver . Attribution And Authentication Help Please

The bubbles and soft features are very concerning to me too.

Yeah sorry but I'm definitely not an expert on buttons. You should check back now and again though as sometimes these things take some time.

I'm quite sure that this current piece is purporting to be Roma/Greek so will move this thread to the ancients subforum.

I am in no way an expert, Roma2021. There is simply something off about the specimen. Especially crude in many ways. The gap in the dotted edge element is strange. Not only are the tiny voids troubling, but also the appearance of (what appear to be) stress fractures on the reverse. As if the coin had been stamped or pressed. A weight and clear edge pic would offer some beneficial information.

The edge picture is a bit blurry but it kind of looks like the remnants of a casting seem that's been filed.

Nobody in Roman territory in Gallienus' time was making large silver coins. For any reason. The silver denarius itself had disappeared, replaced with the "double denarius" which was in fact by this time made of essentially zero percent silver.

Roman Provincial silver, as a whole, is largely unknown outside of a few select locations such as Egypt, Caesarea-in-Cappadocia, Ephesus and Antioch. Silver coinage issue was an Imperial prerogative, rather than under local council control as with bronze coins. You're very unlikely to find Roman Provincial coins in Italy, silver or bronze, in an archaeological context, as they would not have circulated there at all, so a random street vendor isn't likely to stumble upon one.

Finally, here is the bronze coin this was copied from: a provincial of Gallienus from Synnada in what is now central Turkey.