FWIW, it's the same ammo I've always used in it. I think it was said earlier in this thread that the 527 is designed around use of ComBloc ammo. I suspect that it is just a worn spring and that replacing it will solve the problem.The surplus/milspec ammo your using is known to have hard primers. The Tula brand is the same as what they issue to their troops.
I've had the bolt apart, and ran a pipe cleaner through it, and reassmbled it. I have not had the spring removed, but from the youtube video, it doesn't look too terribly hard. Anyway, we'll see how it goes. I'll give an AAR.I'll bet it's not that difficult to break the bolt down for spring replacement. Let us know how it goes.