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...
when i first my 6.5 CM back in '08 or '09, there was no brass to reload for. someone said the 308 Winchester, but it took a couple of steps to do. a 22/250 case necked up to 6.5 is a little short on the OAL, but i think i may as well try it. to my amazement, it worked even tho it was shorter (.2 or .02" i think). i still have the 6.5/250 cases left....somewhere.
i sold the Creedmoor about 6 or 7 years ago, because it got boring. the 6.5 CM was and is a whitetail deer round. i used 120gr Hornady SST/Nosler BT and 140gr Hornady SST/Nosler BT with Superformance powder. the CM would go (for any bullet) 1/2 - 3/4" group at 100 yards (5 shots/bench). when the shooting gods smiled upon me, the CM would do 1/4" group.
the longest shot i took with the 6.5 CM is something like 120+/- yards (i think) on a doe. i've never shot it over 300 yards, but it rang steel.
