Shades of differences: The neck on the 30/06 is shorter than the neck of the Ackley Improved version meaning when a 30/06 chamber is reamed to to the Ackley Improved chamber not all of the old chamber is removed. In the perfect world the Ackley chamber is cut as a new chamber, in the other world the chamber is cut with an existing 30/06 chamber, some drawings list the difference in length between the two case necks as being .030 thousands, the Ackley being the longest.
.030 thousands and it's significances, The old saying that has been handed down since the Internet is not true "Ackley designed the Ackley Improved chamber to head space factory ammo". That part is true but when a 30/06 chamber is reamed to the Ackley Version the shoulder/neck juncture is not removed and if the chamber had XXX amount of head space before reaming factory ammo when fired will still have xxx head space.
Back to the perfect world, the short neck of factory ammo is sized (head spaces) when chambered in the Ackley chamber, when fired the rest of the shoulder and case body is (blown out and forward to form the rest of the shoulder, keeping up with two thoughts at one time, part of the shoulder is formed when the case is chambered) formed, and when blown out the case gets shorter, it does not stretch and the firing pin does not drive the case forward (on my rifles).
F. Guffey
Then the question becomes "Why would I waste your time with details"? 'Shades of difference' the availability of dies and reamers', Ackley neck length is .419, the length of the neck on the 30/06 is .389 + or - a few, point? one die can not size cases for both chambers. For the reamer to remove all of the 30/06 chamber the barrel should be set back, then the 30 Gibbs becomes an attractive choice, the Gibbs reamer removes all of the chamber, but when the Gibbs reamer is used, check the length of the chamber, My Gibbs chamber retains the length of the 30/06, there is an up side, the neck of the Gibbs is .217 + or-, in my opinion the neck needs all the help it can get, if 30/06 cases are used to form the Gibbs cases forget the length advantage, after forming and firing the Gibbs will be .040 thousands shorter than the parent case, because the case does not stretch nor does the firing pin drive the case forward, nor is the shoulder driven forward .202 thousands, part of the shoulder becomes part of the case body and part of the neck becomes part of the shoulder, all of this forming shortens the case when the case body is blown out when formed.
And I still think it is funny, the case, powder, bullet and primer accelerates to a speed equal to the speed of the firing pin to escape the strike, only on my rifles, my primers are crushed before the rest of the components know the primer was crushed.
http://www.z-hat.com/Cylinder.htm
F. Guffey