Blowback and dislodged primers are indicative of plunger style inlines. My CVA Staghorn did the same thing (sans the FPJ), and the spray got worse as you stepped up the powder charge. There is no significant force that holds the primer solid against the breech - only friction and what little force that striker spring exerts at it's full extended (expended) state. All Knight is going to tell you to do is wear eye protection.