I don't have this coin yet, but it looks like an unlisted workshop. RIC only lists Z for Constantine and it does not look like that, unfortunately the reverse is a little rough, but this type is fairly rare.
Constantine I
A.D. 313
IMP C FL VAL CONSTANTINVS P F AVG; laureate head.
HERCVLI VICTORI [To Hercules, the victor] Hercules standing right, right hand behind back, left leaning on club covered by lion’s skin, in left field [?]
in exergue ANT *
RIC VI Antioch 170c