A raid on the premises on an industrial estate in Possilpark, Glasgow, uncovered a secret hidden room containing cash and equipment for processing heroin - but only a tiny package of the drug.
Firearms officers were called in when a pump action shot-gun revolver and an Uzi sub-machine gun tumbled out of a store cupboard - but the weapons proved to be imitations, designed to fire ball bearings.
At the High Court in Edinburgh, judge Lord Bannatyne jailed garage boss Desmond Stewart, 33, for a total of four years and nine months.
Stewart, of Glasgow, admitted being concerned in the supply of heroin and having counterfeit £10 notes under his control.
Solicitor advocate Liam O'Donnell, defending, said the offences were out of character for Stewart who has an almost clean record.
Cash totalling £53,652 was seized, along with a small amount of heroin valued at £20.