A US man accused of posting an assault rifle and a 9mm pistol in the mail to buyers in Australia may have also sold marijuana, hallucinogenic mushrooms and silver bullion through an online black market.

Adam Joseph Bunger, 33, from Bowling Green, Kentucky, is accused of using the German-based encrypted "deep web" website Black Market Reloaded to connect with buyers in Australia, the UK and Europe.

During a bail hearing in Kentucky on Friday prosecutors said Bunger was receiving 100 private messages a day regarding the sales of guns.

"He has no serious criminal history, but, man, he has gone from 0 to 100," assistant US attorney Jo Lawless told Judge Brent Brennenstuhl, the Park City Daily News reported.

"... It's a little mind-boggling.