A number of things can cause pierced primers.  Among them are thin primer caps (or a substandard production run), misshapen firing pin tips, excessive protrusion, etc. 
 
You don't specify the gun you're using.  I assume a Parker.  Still, I'd simply make a switch in brands and see if the issue goes away.  Personally, I prefer Federal 209A.  In addition, I would discourage you from the Fiochhi brand.  Imports tend to have thinner caps.  Especially the vile Cheddite primers.
		 
		
		
		
		
		
		
		
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