My rifle had the 40degree shoulder. I had RCBS make the dies. And the rifle came with Ackly diesSpeer Wildcat manual first printing 1956 has Ackley data for the 244 Improved and he used 1/12 twist and it has 30 degree shoulder. In Ackley book the original 244 improved had 26 degree shoulders with a minimum body taper. (They don't show what that was but in Speer book they have case dimension.) Later they changed shoulder to 40. In Ackley book standard twist 1/12 and special twist was 1/10
The loads in Ackley book for the 244 Improved, some of the loads are same as in Speer Manual.
I used 1/10 in 6RemAI.
I still have the dies and form brass. They look like weatherby cases. The shoulder is round not s sharp angle.