This coin just does not look like any Constantine I have ever seen. Is it a barbaric copy, or what is it ?
This is not Constantine but his father Constantius I aka Constantius Chlorus. You can find a few similar coins on his wildwinds page.
That’s because it’s his father Constantius. legend reads: CONSTANTIVS NOB CAES It is an official coin. @red_spork just beat me to it.
Sorry I think I found it. Constantius I as Caesar Post-Reforem Radiate Antoninianus, Rome. FL VAL CONSTANTIVS NOB C, radiate, draped, cuirassed bust right. VOT XX Gamma in three lines within laurel wreath. RIC VI Rome 87a
Warren Esty (@Valentinian) has some info on these here: http://augustuscoins.com/ed/VOTA/tetrarchy.html#Carthage My Max version lacks an officina. Probably Rome mint.