There were some issues early on with misfires in the Ruger Mini 14's in 7.62 X 39 MM, with some steel cased Russian ammo. This was due to the Russian ammunition having harder primers than the commercially produced brass stuff in this country. The original 7.62 X 39 MM Mini's had a somewhat weak firing pin spring, that would produce misfires with some brands. This added to the problem.
I ran into a guy shooting one at the range several years back, with some steel cased Russian stuff in a Mini. And he had well over 2 dozen rounds sitting on the bench, out of over a hundred rounds that he ran through the gun that didn't fire. You could see the primer indentations were very shallow. I put them into my Yugo underfolder, and they all ran fine.
I gave him mag full, (30 rounds), of the Golden Tiger 7.62 X 39 MM I was shooting, and every one went bang in his gun. So I swapped him 100 rounds of my stuff for his, and he had no more issues.
I read where Ruger has since fixed the problem. I'm assuming they installed a stronger firing pin spring. As most everyone with a 7.62 X 39 rifle is going to shoot steel cased ammo of some type in them.