Maybe you or someone else on this forum can explain why an ackly improved cartridge reaches a higher level of performance than its original one with standard degree on the shoulder. I have to disagree with you that the shoulder angle has little to no bearing on a cartridges performance. ctw
There are two reasons Ackley Improved cartridges (or any Improved cartridge design, as many others "improved" cartridges but Ackley is the most famous) are faster than their unimproved parent cartridges. In my opinion, the primary reason is usually pressure levels. The secondary reason is the case volume is made larger by reducing the body taper and moving the shoulder forward. As for the primary reason, that's been a topic of debate for years, with folks denoting that pressure signs don't show up in the Ackleys until velocities are much higher than their parent cartridges, indicating huge gains without pressure issues. But this is a false equivalency, because the reduced body taper (straighter case walls) and steep shoulder cause the pressures to be exerted more in a radial fashion (outward into the side walls of the chamber) than a linear fashion (rearward as thrust against the bolt face), so the real pressures are marked, and typical Ackley velocities from PO's work and from other sources not testing things with pressure reading equipment, push those Ackley rounds up around 70-75kpsi, where the parent rounds are running 60-65kpsi, generally, and sometimes less. Consider the old argument that the 280 Ackley Improved is "all but equal to the 7mmRemMag." For that to be true, the Ackley (case capacity of 64.8gr of water, as per Nosler) would have to run significantly higher pressures than the 7mmRemMag (case capacity of 78gr as per Nosler) to achieve the same velocities. And in Nosler's pressure tested data, the Ackley indeed runs ~150fps slower than the RemMag, because case volume and pressure are the two key ingredients in developing velocity, if barrel length is kept even. Adding in the 280Rem (case capacity 62.5gr) with velocity about 80fps below the Ackley, and you see where the real key is - case volume. Even more impressive in this comparison is that the 280Rem and 280AI were both tested in 26" barrels, while the 7mmRemMag data was developed in a 24" barrel, giving even more edge to the 7mmRemMag's additional case volume.