I got you now. But wouldn't it just be easier to try different primers to see which one gives the best fit??

I tried different ones in my Knight rifle. Then I believe the bolt also applies a slight crush fit to the primer. So I get absolutely zero blowback without doing any shimming or such.

Does this make the crush fit a slightly better system?? I did notice that when the primer fit better I had less crushing of the primer. Still a slight crush, but not nearly as noticable as other primers.

I have Sabot Loader to thank for that little bit of information. He showed me exactly how to get my primer to fit perfectly. I was actually suprised that after 25 shots of Black Horn I had absolutely zero residue of any type anywhere on the bolt or any other part rear of the inside of the breech plug. I was very happy with that. Tom.