Officers have also charged a man believed to have been his accomplice.
Detectives initially charged the 28-year-old Embleton resident with armed robbery, but Warwick Senior Sergeant Brad Burnett said recent inquiries resulted in another charge.
He alleged the man returned to Dunmore Circuit on June 2, after robbing the victim and threatened him as he held a shotgun to his head.
Sen-Sgt Burnett said the man left in a 4WD which was driven by his co-accused.
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READ NOWHe was charged with aggravated armed assault with intent to rob, adding to his initial armed robbery charge.
A 30-year-old man from regional WA was charged with the same offences.
Sen-Sgt Burnett said pressing a gun to someone’s head was considered assault even if nobody was injured.