"I am pretty good after all," Dahlby said in a interview with Sveriges Television after the result was confirmed.
46-year-old Dahlby had an almost faultless final, missing only once, to climb from fifth and into the silver medal position.
Four years ago in Beijing, Dahlby was the world number one but failed to qualify for the final and he told of his motivation to ensure that there would be no repeat four years on.
A shaky qualifying shoot left him trailing the leaders however at The Royal Artillery Barracks but Dahlby was able to find his best form at the right time and secure Sweden's second silver medal of the games.
Britain Peter Wilson meanwhile grabbed the home nation headlines and Great Britain's first Olympic shooting gold in 12 years.
The world record-holder thrilled packed galleries at the Royal Artillery Barracks, hitting 188 targets out of 200 to win the double trap.
The towering Wilson took up double trap in 2006 and is trained by Sheikh Ahmed al-Maktoum, a member of Dubai's royal family and gold medallist at the 2004 Athens Games.
The 25-year-old was impressive in qualifying in first place for the final, with 143 hits out of 150, but faced fierce competition in the final, involving a further 50 targets.
Russia's Vasily Mosin, who won the bronze after a shoot off, put huge pressure on
Wilson but the red-capped Briton, standing six feet six inches (1.98m) tall, held his nerve to hit 45 targets and claim gold, two clays clear of Dahlby.
Wilson admitted he felt under intense pressure as he saw his lead cut to just one clay at one point.
"Of course you're trying not to focus on it too hard but you're just going through my technique," he said. "I spoke in depth with my coach, Sheikh Ahmed and we made a plan. I felt I tried to execute it as well as I could."
In bright and breezy conditions, every shot by Wilson, who wants to set up a business around shooting that funds him and enables him to continue the sport, was cheered by the packed stand, including the watching Princess Anne.
Wilson is the first medallist in shooting for Britain since Sydney in 2000 when Richard Faulds, who failed to make the final on Thursday, won gold in the same event. Britain also won a silver that year in the men's trap.
In double trap, two targets are released simultaneously from trap machines, travelling at different heights and angles. A round consists of 25 doubles. The shooters fire one shot at each target.
After six days of shooting competition China, the United States and South Korea lead the way on two golds apiece. China have won the most medals overall.