The radius-ed shoulder was developed in the 1940s in Germany and the US simultaneously. The PMVF, Powell Miller Ventrified freebore became the CCC cartridges Controlled Combustion Chambering. Vom Hoffe and the German military experimented with a couple of variations. Powell and Miller I think were first in Ventura California and then moved shop to Hollywood, I believe they became the Hollywood gun shop that made dies and presses as well as custom rifles.
Roy Weatherby was no doubt influenced by their work, in the 1950s he developed the double radius shoulder, the early ones had been single radius but had radius-ed the neck and shoulder but not both. PMVF and CCC gave Roy the idea for free boring the chamber as well. The double radius allowed Weatherby to patent and trade mark the design.
They claimed to believe that the radius acts as a venturi tube to accelerate gas flow. It was also a marketing feature and made it more difficult to copy by other gun smiths before it was patented. Testing has proved this not to be true but has shown the shoulder angle of around 30 deg. to produce more uniform pressures which is signifigant when running near maximum pressure.
CCC 30-06 Imp.
http://www.cartridgecollector.net/30-06-cccHere is an old thread on the topic where I made the same points:
https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/3571724/1
