An Apparently Very Rare As Of Julia Maesa - Pudicitia

Both the "copper" As and the orichalcum dupondius are increasingly rare beginning with the reign of Septimius Severus. The copper coins become bronze and both the dupondius and sestertius are usually referred to as simply being "brass". Just a higher grade of bronze really. By the AD 220's the metals became nearly indistinguishable.
One major reason all the 'bronzes' (esp. dupondius) of the period become scarce is that they were recycled by the emperors who followed the Severans. Melted down and reissued as the increasingly smaller sestertius by Gordian III & Philip.
Alexander Severus made an attempt to restore the dupondius and Trajan Decius tried to make the double sestertius a 'new' bronze denomination. Both efforts failed and were short lived. The sestertius of the AD 250's were usually around 16-18 grams of recycled (lowgrade) bronze. Sometimes even as small as 13 grams. By AD 260's Postumus made one last attempt at issuing 'good' coins in his Gallic Empire.
It failed
Aurelian tried again
He failed
Finally Diocletian threw out the whole system and started over again from scratch.
It worked for twenty years before collapsing !
A truly remarkable achievement for the period.