First thought was Septimius Severus, but it is hard to tell what is crud and what is coin. What is the reverse like. Any chance you can clean up the legend a bit?
Size and weight? Reverse? I don't think that's a mustache. It's dirt/corrosion. I can make out IMP CAES M (A)NT (G?)..... Best guess is Gordian III. The overall face and nose shape looks rather like him.
I make another picture 9g 27mm Coin looks much better live. I need something like dougsmith have for pictures
Maybe this. RIC 254 Gordian III AE Sestertius. 238-239 AD. IMP CAES M ANT GORDIANVS AVG, laureate, draped & cuirassed bust right / FIDES MILITVM S-C, Fides standing left, holding standard & transverse sceptre. RIC 254; Sear 8706; Cohen 88. http://wildwinds.com/coins/ric/gordian_III/t.html
This is look like "standard" But for sestertius they say it's 30-35mm This one is only 27? On wildwind There is no other standard exept antoninianiss or denarius
Wildwinds does not have every example of every coin. You should also have a look at acsearch and coinproject.