Police found a corroded sawn-off shotgun, another shotgun in poor external condition and an antique pistol during a search at Richard Watt's home.
Watt, aged 76, admitted firearms offences, including possessing a prohibited weapon and possessing a gun while not holding a shotgun certificate, when he appeared at the High Court in Edinburgh.
A judge told the former gun enthusiast: "These are very serious offences that you have pled to, as I have no doubt you appreciate."
Lord Burns said: "Unless exceptional circumstances exist, a minimum sentence of five years should be imposed."
Advocate depute Susanne Tanner told the court that Watt had no previous convictions and was the main carer for his wife, Patricia, who is registered disabled. The prosecutor said that in September last year police searched the couple's home in Corthan Crescent, Aberdeen. She said: "A double barrelled side by side shotgun and ammunition and various other items relating to the manufacture of ammunition were observed on open display."
Defence counsel Jonathan Crowe told Lord Burns that he intended to make a plea that exceptional circumstances did exist in the case which allow the minimum sentence to be avoided. He said the guns had been kept in relatively secure conditions and there was little chance of them "falling into the wrong hands".
Lord Burns deferred sentence for the preparation of a background report.