Little confused about what happened here. Did the firing pin release as you were engaging the bolt and before it was fully locked up?
How can you have a “slam-fire” in a bolt action? The real difference between NATO 5.56 and 7.62 and commercial .223 and .308 is the chamber pressure. NATO loads are fairly mild compared to some commercial loads, and NATO-spec guns are designed for NATO-strength loads. Same thing with M1 Garands that get blown up with commercial loads.
As I rotated the bolt, the round fired. I suspect the narrow throat prevented the brass from seating properly in the chamber. The bolt deformed the case head just enough as it was locking into place to pop the primer. The head spacing was simply wrong for that brass in my Police Special .308 chamber.