I formed brass from 9.3x74R. Trouble is, the WR version of the .400/.360 has a thicker rim (about 0.063"), so headspace is problematic. There's not enough shoulder to do the job. That's why I was looking for another cartridge with a thicker rim and compatible dimensions otherwise.

For the Purdey version of the .400/.360 the 9.3x74R is just fine. I'm currently doing that conversion for a nice DR to recently come into the fold. I'm planning a report on this DR in the near future after a little more range time and some photography.

Curl