I am always amazed that people still considered Ackley's book a source of reliable data. A lot of the loads were a grab-bag from "various sources" (I believe that's the phrase used in the book), and some he acknowledged were estimated by the wildcatters who developed pet cartridges.
A few of the loads he personally tested were probably OK, but the more I learn about pressure-testing the less I trust any data from that era. A lot of people simply didn't know how to conduct repeatable and controlled pressure tests, which is why Speer used case-head expansion as their method, after nobody working there could figure out out to work copper-crusher equipment.
There are also two other factors: Nobody knows what bullet was used in most of the data in his book, or the primer, case, etc. And the powders used not only aren't exactly the same anymore, but the storage conditions are unknown.
There are a bunch of other errors in that book, which I won't go into since they're too numerous. It's an interesting slice of history, but not a trustworthy source of loading data.
It becomes less amazing when you note his method was remarkably similar to yours, "based on all the usual signs". He stated using the same method. This is probably more significant than comparing 6mm, 25-06 etc. If we have no way of determining between the calibers chamber being identically proportionate to scale, the comparison becomes less meaningful if not meaningless. I suspect it more important to limit pressure to the weakest link of the equation, be it the action, brass, chamber of each. It is for this reason I would suggest double checking a load before accepting a maximum as ok. I certainly could have said it better, and should have. As to Ackley's book, I mostly only refer to it when he's the
A in
AI due to the before mentioned varied results.
