BR4s are not hard so much as they have a thicker cup than others.
Back in the days of converting 308 range rifles (no change to firing pin hole in bolt) to 6MM BR for F Class it was quite common to have pierced primers. We all changed to BR4s and the problem disappeared.
The chart below is now quite old but probably still accurate. I have never had any problems with BR primers or any primers for that matter. Are you seating them fully to the bottom of the primer pockets?
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