Yeah they dont like us doing that due to the fact that if you adjust it to much and slam the gun shut, it will in fact go off.
Keep it simple, adjust for only the brand of primer you start with and strictly use that.
It will stop the blow by solid as shown in the video CVA Firing Pin Bushing Shim Kit - YouTube
If you'd like to make it easier on you but a little more up keep, try the metric O rings
. The code # you need is on the picture.