Pardon my ignorance but I don' t see how this could be a head space problem when it occurrs with a dummy round. You didn' t say how old the rifle is. Is it within the warranty period? If so send it back. Otherwise have a smith look at it for sure. It is strange that the problem which used to occur only periodically now happens regularly. I had a model 70 that behaved this way when new. The ejected casing had noticeable gouges in it. Mine was cured by polishing the chamber. gg.