I remember an article in Shooting Times where Rick Jamison (if I spelled his name correctly) shot his rifle and then re-chambered it to the next cartridge.
It showed that the velocity gain was modest from the 30-06 to the 30-06AI and then the 30Gibbs, When loaded to the same pressure!
I'm no expert, I just read the magazine several times as it had an article on 22-250 1-8 twist.
Just a question, does the Gibbs actually clean up the shoulder of an Ackley ?
The examples of Gibbs cartridges I’ve seen have diameters closer to the Standard .441”, just pushed forward some. I’ve also seen some which were actually botched Ackley rechamberings, with .455” shoulder diameter.
Created without being properly set back and then reamed forwards deeper,
to create an Ackley/Gibbs chamber. Usually involving similarily bubba’d dies
