Yes I also have read Mikes articles.
Used 215 feds as well as pistol and even berden primers reloading the .43 Spanish shells. Yes there is a difference in accuracy using different primers. I even silver soldered the boxer primer pockets flash hole shot and drilled a flash hole like the berdan flash holes and they shot well doing this but not worth the time converting the flash holes.
As far as the bullet getting pushed ahead with the primer making a fouling ring,,,,well I breach seat often and I pushed the bullet ahead of the case mouth as far as 1/8" and never seen any difference with fouling just better accuracy
The card wads under the primer in the primer pocket and as well under the powder ov er the flash hole the only good results I seen with my Sharps and Stevens are good flame cuts on the face of these two breach blocks from the back pressure of the primer ignition blowing back past the primer cup.
And I will say that the primers fit tight in the pocket.
And yes I'm also guilty shooting holes through a 36 Plymouth 4 door sedan using my .43 Spanish roller
even busted a hole through the flathead water jacket.