My experience has been quite different from that treatise. I've seen a lot of 30/06 and similar cartridges back the primers out with excess headspace in blot action rifles. And the fact that he was using factory loads in the 30/30 AI using the AI chamber didn't change his often proven statement. As soon as the cartridge expanded to the near straight walls of the chamber it no longer went backward.
The AI loads he published were much higher than the 42K pressure. I chambered a Ruger #1 for it and pushed his loads a little higher still. I used the 3200 fps 110 grain load in a Marlin 336 I chambered, for prairie dog hunting. It would blow a primer pocket on occasion in the sun.
Also, I disagree with his claim that lubing a case will not make it thrust rearward. I've had many customers over the years just do that with their guns with headspace. Lubing the cases, moved the shoulder forward and took care of the problem. Just had to back up the sizing die a bit. The fact that excess headspace will back a primer out against the bolt fact on any rifle, is proof that there is relatively little bolt thrust except in a lubed chamber & case. Then the primer stays flush, and the shoulder is moved forward as the case moves back against the bolt face on firing.
That's my experience with it. Many of the AI rounds weren't much of an improvement, but some including the 30/30 definitely were. The so called .223 improved wasn't much better than the original round.
