I'll throw this visualization into the fray. I drew this up in AutoCAD. The Ackley Improved Dimensions are from Ken Howell's book and are based on dimensions from the Speer No. 4 Manual. I believe this was before SAAMI standardization. If you don't set the barrel back you will end up with a fire-formed cased that has two shoulder angles (ask me how I know).

[Linked Image]