He did mention in an interview once that he wished he had become famous for inventing an agricultural machine instead: "Blame the Nazi Germans for making me become a gun designer. I always wanted to construct agricultural machinery."
The BBC article I read on this mentioned something similar although it was more along the lines of he said didn't make any money from the gun, he would have been better off (made more money) by designing a lawn mower.
I'm pretty sure it didn't have anything to do with the money, but his desire to improve production rather than destruction. Here's an article with the lawn-mower comment you're thinking of: http://www.theguardian.com/world/2002/jul/30/russia.kateconn...
Another comment of his (quoted in the thestar.com article above) suggests that he didn't think much of making money from inventions: "At that time in our country patenting inventions wasn't an issue. We worked for Socialist society, for the good of the people, which I never regret".
Quoted in this artice: http://www.thestar.com/news/world/2013/12/23/mikhail_kalashn...