The inventor of the Kalashnikov assault rifle apparently wrote to the head of the Russian Orthodox Church before he died expressing fears he was morally responsible for the people it killed.
Mikhail Kalashnikov, who died last month aged 94, wrote a long emotional letter to Patriarch Kirill in May 2012, church officials say.
He said he was suffering "spiritual pain" over the many deaths it caused.
Kalashnikov had previously refused to accept responsibility for those killed.
But in a letter, published in Russia's pro-Kremlin newspaper Izvestia, he wrote: "My spiritual pain is unbearable.
"I keep having the same unsolved question: if my rifle claimed people's lives, then can it be that I... a Christian and an Orthodox believer, was to blame for their deaths?" he asked.
"The longer I live," he continued, "the more this question drills itself into my brain and the more I wonder why the Lord allowed man to have the devilish desires of envy, greed and aggression".
The letter is typed on Kalashnikov's personal writing paper, and is signed with a wavering hand by the man who describes himself as "a slave of God, the designer Mikhail Kalashnikov".
The Kalashnikov, or AK-47, is one of the world's most familiar and widely used weapons.
Its comparative simplicity made it cheap to manufacture, as well as reliable and easy to maintain.
It is thought that more than 100 million Kalashnikov rifles have been sold worldwide.
Kalashnikov refused to accept responsibility for the many people killed by his weapon, blaming the policies of other countries that acquired it.
However, pride in his invention was tempered with sadness at its use by criminals and child soldiers.
"It is painful for me to see when criminal elements of all kinds fire from my weapon," Kalashnikov said in 2008.
Defend his country
In his letter to Patriarch Kirill, Kalashnikov said that he first went into a church at the age of 91 and was later baptised.
The BBC's Steve Rosenberg in Moscow says it is unclear how much of it he wrote himself. Izvestia quotes Kalashnikov's daughter, Elena, as saying she believes a priest helped her father compose the letter.
The press secretary for the Russian Patriarch, Cyril Alexander Volkov, told the paper the religious leader had received Kalashnikov's letter and had written a reply.
"The Church has a very definite position: when weapons serve to protect the Fatherland, the Church supports both its creators and the soldiers who use it," Mr Volkov was quoted as saying.
"He designed this rifle to defend his country, not so terrorists could use it in Saudi Arabia."
Kalashnikov received many Russian state honours, including the Order of Lenin and the Hero of Socialist Labour, but made little money from his gun.
He died on 23 December after being admitted to hospital a month earlier with internal bleeding.