Authenticity Check On A Claudius As

You folks could do a lot toward furthering my education in ancients by chiming in on this As. To my untrained eye, the patina seems odd although I could be wrong. In some indescribable way the bust doesn't look right - nor does it match exemplars from various auction sites and the same goes for the 'S' on the reverse. Finally, is it typical to have such misshapen letters as can be seen in 'Caesar'? The weight is not known, the diameter is 26mm. Credit for the images goes to the seller.