Noel Wheatley, 30, carried out the robberies in Bearsden and Hardgate on February 11, this year, to pay off a drug debt.
At Scotmid in Ledi Drive, Bearsden he presented the shotgun at two employees and robbed them of £780.
Wheatley then targeted Ladbrokes in Glasgow Road, Hardgate where he threatened a woman employee with the weapon and made off with £301.45.
The High Court in Glasgow heard that Wheatley was handed the shotgun by men he owed drug money to and told it was not working.
Jailing Wheatley judge Lord Boyd said: “I accept that you were given the gun by another and the gun was not viable, but it was your choice to carry out these offences.”
Lord Boyd told Wheatley the sentence should act as a deterrent to prevent robbers thinking that shop workers were ‘an easy target.”