Wheelchair-bound Andrew Darroch, 59, of Paisley, received a more lenient sentence than the minimum tariff for the offence after a judge heard of his medical problems.
Darroch had admitted possessing the weapon without authority in 2010.
Yesterday the High Court in Edinburgh heard how he had been praised by police for foiling an arranged pitched battle between Celtic and St Mirren fans. He was also commended for installing CCTV in a bar he owned.
The court heard Darroch blamed a tenant for what had happened but realised he should have handed the sawn-off shotgun over to police immediately.
Instead, he had delayed and was caught with the weapon in his office. The gun was in poor condition, but could still be fired.
Darroch had previously lodged court papers naming another man as the owner.
Sentencing, Lord Brailsford said: "It is not the most persuasive explanation I have ever heard. Nevertheless I accept it."