It aint so much just a "hard primer problem" as it is that Russian/Eastern Bloc chambers are spec'd slightly different than US/Western chambers. And to make matters worse, Ruger uses it's own reamer which is patterned after a somewhat "one off" French design. Plus, most of the time you'll find that the primer in steel-cased ammo sits slightly lower in it's pocket than does the primer in brass ammo....so then there's that.
When ya add all of that together, what you get is a steel cased cartridge which may or may not be sitting in the Ruger chamber just right and a primer which almost always sits too deep in relation to the rifle's available firing pin protrusion...which by design, is much shorter than the firing pin protrusion of an AK or SKS.
So yeah, unless you're real lucky relative to "tolerance stacking", you're going to experience miss fires when trying to use Commie-made ammo.
In other words, Ruger knows more about their 7.62X39 guns than most folks give 'em credit for. Hence the warning to only use ammo made to US specs.
And BTW, Mini-30 owners have been fighting the same fight for years, so welcome to the party. :lol: :lol: .
DGW
