Well, you need to look again, since this drawing is listed at both The Reload Bench and Steve's Pages as the 30 Gibbs with a 27 degree shoulder. The Ackley shoulder, when done by Ackley, is set at a 40 degree angle.
If you had read my entire post, you would have understood that I don't believe that it is a correct version of the Gibbs anyway due to the overall length and the shoulder angle. These two drawings were done by Dave LeGate for Rifle and Handloader magazines and taken off of fired cases. The contention is that the measuring was not very accurate. The newer drawing done by Dave is very close to what most of my chambers cast to. It is all that I could find quickly for posting.
But since you now seem to be an expert on both the Gibbs and the Ackley, you can ignore both of these posts and continue on your merry way.