Military busts are not common on the antoninianii of Maximianus Herculius. His later issues changed the PAX AVGG types from the usual Pax standing left, with Victory on globe and scepter to a Minerva type. Maximianus Herculius - Antoninianus Obv:– IMP MAXIMIANVS AVG, Radiate, helmeted cuirassed bust right Rev:– PAX AVGG, Minerva standing left, olive branch upward in right hand, spear in left and resting left hand on shield Minted in Lugdunum (//A). Emission 10, second series, Officina 1. 1st March A.D. 293 – 20th November A.D. 293 Reference(s) – Cohen 427. Bastien XI 503 (15 examples cited). RIC V Pt. 2 -. A nice example with some silvering remaining.
While looking for rare militaries you might find the slightly more common Consular busts. The tip off is the eagle scepter and fancy fabric in the robe.