John Lowe, who killed Christine Lee and Lucy Lee in February, was given a minimum sentence of 25 years.
The jury at his Guildford Crown Court trial was told Lowe wanted the women "put down".
Surrey Police has apologised for returning Lowe's confiscated guns to him seven months before the shooting.
Sentencing Lowe, Mr Justice Singh praised the "extraordinary courage" of Lucy Lee after she returned to face her killer after making a frantic 999 call.
He said that, having heard the evidence, he had come to the "clear conclusion" the 82-year-old had intended to kill both of the women.
"You shot Lucy Lee in the back of her head after she made the 999 call, then reloaded your gun and pursued her outside the cottage, with the intention of making sure that this time she died," he said.
In a victim impact statement Stacy Banner, Lucy Lee's sister, said she was "haunted by what Lowe has done".
She said Lucy was the "big sister who comforted and preceded me" and the murders had left her struggling to eat and sleep.
Outside court, she said: "I'm relieved it's over. He's never getting out."
Ms Banner has criticised police for returning guns to Lowe just months before he carried out the shootings.
Surrey Police has admitted the decision "was flawed and did not meet national standards".
Three Surrey Police employees are being investigated for gross misconduct by the Independent Police Complaints Commission (IPCC) over the decision to return the weapons.
Christine Lee's sister, Julia James, said she felt "despair, physically and emotionally" since the death of her two relatives.
"I miss them more than I can say," she said.
At the start of the hearing, prosecutor Mark Dennis QC said Lowe's advanced age should not "dramatically" reduce his sentence and the "starting point" for a double murder of this kind would be a minimum of 30 years in jail.
Surrey's Police and Crime Commissioner Kevin Hurley said as the trial was now over the inquiry could focus on why Lowe was given back his guns.
Factors which would be investigated included whether the decision had been made because of "human error by negligence, as a genuine mistake, or as a result of funding cuts to backroom staff", he said.

FRHI Holdings owns three of the world's most famous hotel brands: Fairmont, Raffles and Swissôtel.
It has 155 hotels in 34 countries, with 42 in North America, including The Plaza in New York.
AccorHotels, which owns the Novotel and Ibis chains, said the purchase would give it a better-balanced profile.
The owners of FRHI include the Qatari Investment Authority and the Kingdom Holding Company of Saudi Arabia.
They will become major shareholders in Accor, with stakes of 10.5% and 5.8% respectively.
Accor will pay for the acquisition by issuing 46.7 million new shares, worth about €1.8bn based on Wednesday's closing price, and a cash payment of €786m.
The French company already owns luxury hotel brands including Sofitel and Pullman, as well as the mid-market Novotel and Mercure, as well as the budget Ibis and hotelF1 chains.
It said the deal would increase profits from the second year after the deal was completed, with €65m in revenue and cost savings expected.
Sebastien Bazin, chief executive of AccorHotels, said: "It offers us robust and global leadership in luxury hotels - a key segment in terms of geographic reach - growth potential and profitability, for long-term value creation."
"We are positioning ourselves as a key player in the current industry consolidation process while maintaining substantial leeway to implement our transformation plan."
The deal is the latest consolidation in the global hotel industry after Marriott International made a $12bn takeover of Starwood Hotels & Resorts to create the world's largest hotel operator.
FRHI was put up for sale earlier this year by its owners. It was reported in September that London-listed InterContinental Hotels Group was considering making a bid, but none materialised.
Sheikh Abdulla Bin Mohammed Bin Saud Al-Thani, chief executive of the Qatar Investment Authority, said it looked forward to becoming a significant shareholder in Accor.
The QIA will get two seats on the Accor board, while Kingdom Holding will have one.
An 82-year-old man has been jailed for life for murdering his partner and her daughter who he shot at close range at his puppy farm in Surrey.
[NEXT_CONCEPT]
The owner of hotels including the Savoy in London and Raffles in Singapore has been bought by Accor for €2.6bn (£1.9bn).