I was curious about the history of the improved 257 Roberts. I am curious about the chronology of the RCBS 28 degree version as opposed to the Ackley 40 degree version? Thanks, Peter.

The closest guess on dating comes from the Cartridges of the World and all that is said that is many variations of a 257 improved cartridge surface in the 40's and 50's and the 40 degree Ackley version is the most well known.
In Ackley's own book he states there are many versions, but the 40* seems to be the most well known. Maybe someone who "lived" the introduction could shed some more light on the subject.

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