Recently a co-worker mentioned that he had fired a .300 Ackley Mag, and asked if I knew what it was. I guessed , and told him it was a guess, that it was the .300 H&H with straighter walls and a sharper shoulder. Right or wrong?

You are correct. Generally, Ackley used minimum taper (about 5/1000ths per inch) and a 40 degree shoulder for most of his cases.

dclark