The common factor is the heavy ball ammo. I am curious if there is a load difference other than the heavier bullet weight or a muzzle velocity difference that would (possibly) help to explain this. I am aware that the actual loading spec is just a "guideline" for much of the ammo produced and has no real meaning in the real world (sorta like the commie version of quality control); but the question remains as "why the heck does only heavy ball give multiple rifles the same problem". I have no clue so it's time to ask.