Try making sure that all of your primers are fully seated with the face of
the primer slightly below the surface of the case head. I have experienced flat primers before with handloads with CCI primers that were not fully
seated because of the very tight fit in the primer pocket. I no longer buy
CCI primers because of the extra effort required to seat them. Some of
then were severely flattened even before being fired. Flattened primers
from excessive pressure do not occur at magnum handgun pressure
levels. Most loading manuals have good information on primers and
pressure signs in the information section preceding the load data.