A few comments:
The first cartridge to use the ".30-06" head/rim diameter was the Patrone 88, the cartridge introduced in the German Gewehr 88. It eventually morphed slightly into the 8x57, and the rim diameter was actually nominally 12mm, since Germany used the metric system. After that the Patrone 88 head-size was used in other Mauser rounds, including the 7.65x53 "Argentine" (1889) and 7x57 (1892), long before the U.S. Army brought out the .30-03 and .30-06. (Our army had a habit of copying other stuff in those days. As I've noted elsewhere, the cartridge we usually call .30-40 Krag is almost a carbon copy of the .303 British, which appeared several years before the .30-40.)
There have been other copies of various commercial rounds on the same head-size. The .30 Thompson/Center was far from a really original idea, since it's basically a slightly longer-necked version of 1920's .300 Savage, including the 30-degree shoulder angle.
Yes, Hornady claims the 6.5 Creedmoor is based on the .30 T/C necked down, but the 6.5 Creedmoor is also almost identical to the wildcat 6.5/.250 Savage RCBS Improved, which had a 28-degree shoulder angle.
And all of those mentioned have the 12mm rim diameter of the 136-year old Gewehr 88...
