The northern Swedish pensioner and his son were asked to pull over after customs officials suspected they had travelled down to the university city to arrange an automatic weapons deal, Sundsvall Tidning reports.
In the car officials found the barrel of a gun, a cover for a Finnish automatic weapon and a price estimate.
When taken in for questioning, the 76-year-old said that the quotation related to the machinery necessary for the construction of automatic weapons.
In the 1980s he had designed a weapon for the Finnish army and remembered exactly how it should be put together, he said.
In Uppsala he and son agreed to meet the Polish representative of a Germany company that wished to produce the weapons.
A raid on the pensioner’s house later revealed a vast array of weapons parts, including all the components of a Russian machine gun.
Both men deny committing an offence, arguing that they were trying to reach a deal on the sale of ordinary workshop tools and that no money, blueprints or weapons parts ever changed hands.