Since the Gibbs and the A.I. are both being compared, let me add someting that I think is relevant.
I shot a 6.5-06 A.I. for years and loved it. I took a pile of game including about 25 elk, moose, black bear, and countless deer.
After shooting out the second barrel, I decided to build a Gibbs to increase the performance over the A.I. I went so far as to order brass from Quality cartridge. When I held the brass in my hand, I realized how very short the neck was, and the wheels started turning. I liked the velocity of the Gibbs but much more preferred the A.I. design. Thats exactly how the very first Sherman was born back in 2008.
I used the 270 case to gain length for both capacity and still have a nice long neck.
I blew quite a bit more taper out of the case than even the A.I. and moved the shoulder forward of the A.I. as well.
The result was near identical case capacity of the Gibbs and still had a nice long .300" neck length. Far more than the Gibbs!
I say this because we've since built this case
on every bore size from 25 to 375.
Here is an example of performance:
338 Sherman with a 250 Berger and 24" barrel. 2810' with my hunting load and decent case life.
300 Sherman with a 28" barrel and 190 grain bullet. 3050' with good case life.
Brass is easy to form and has very little stretching after forming.
IMO, its the most you can get for all around performance with an '06 bolt and is a near equal to a belted mag with less recoil and better barrel life.
below vs '06