The Los Angeles Times wrote an interesting article:

Report: AK-47 inventor Kalashnikov was tormented over gun’s toll

“My soul ache is unbearable and has one irresolvable question: if my rifle took lives, does it mean that I, Mikhail Kalashnikov, aged 93, a peasant woman’s son, an Orthodox Christian in faith, is guilty of those people’s deaths, even if they were enemies?” reads the letter, according to the Russia Today translation of the Izvestia story.

“Good and evil coexist side by side, fighting and, worst of all, they resign themselves to each other in the hearts of people – that is what I have come to at the end of this earthly life,” Kalashnikov reportedly wrote to Patriarch Kirill.

A spokesman for the patriarch’s office confirmed the letter dated April 7, 2013, was authentic and that Kirill replied to the vaunted inventor that the church regarded the AK-47 as a weapon that justifiably defended the country during World War II and post-Soviet conflicts.

“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,” patriarchy spokesman Alexander Volkov told Izvestia [link in Russian]. “He designed this rifle to defend his country, not so terrorists could use it in Saudi Arabia.”

Kalashnikov, who was an atheist throughout his adult life until embracing the Orthodox faith of his peasant parents at age 91, had previously rejected the notion that he bore responsibility for the use to which militants and terrorists put his sturdy automatic rifles with the signature banana-shaped magazines.

“I sleep well. It’s the politicians who are to blame for failing to come to an agreement and resorting to violence,” Kalashnikov told the Associated Press in a 2007 interview on the 60th anniversary of the AK-47′s production.
Source: http://www.latimes.com/world/worldnow/la-fg-wn-kalashnikov-guilt-patriarch-20140113,0,5599341.story#ixzz2qJjsgaw9

Kalashnikov should have remembered Luke 22:36 and all the other bible verses that encourage self-defense.

Besides, what is he thinking? That without the AK-47 there would be peace on earth? Ask Cain who killed his brother Abel with an “assault-rock,” an “assault-fist” or a “military-style thick branch.” The Bible doesn’t say what instrument he used.