From OUTDOOR LIFE, this is the story about the development of the 6.5 Creedmoor.  

This is one of the LAZZERONI range of cartridges. It is one of two that does not have its own headstamp, but the 6.17 Flash uses the SCRAMJET case

Relatively old wildcat cartridge based on a shortened 6mm Remington   

Match cartridge designed by Robert Whitley in 2007. Not to be confused with the 6x47 Federal, which is the 222 Magnum case opened up to 6mm, the 6 x 47 Lapua is based on the 6.5x47 Lapua case necked down to 6mm.             ...

   At one stage this development formed part of the US SAW (Squad Automatic Weapon) program, but tests with the 222 Magnum case opened to 6mm with commercial bullets, different propellants and various over-all lengths did not show sufficient progress to...

Also known as the 644 SUPER, this is a match cartridge similar to the 6mm BRX, but with a longer case   

Based on the 250 Savage necked to 6mm. Comes in different shoulder angles   

Can almost be classified as one of the "first" attempts by American wildcatters with the 6mm. This is the standard 250 Savage case necked down to 6mm with no other changes. Various versions of 6mm experiments exist based on the 250 Savage case, as well as the 243...

   Based on a shortened 243 Winchester case

222 Remington necked to 6mm with no other changes   

The no h/s version is an early Western prototype

   Developed by White Oak Armaments, this is an improved version of the 6mm HAGAR.

Part of a series of cartridges. This one is based on the 6.5 Rem Mag necked down to 6mm   

Older wildcat and is a rimmed version of the 6mm Remington   

The .244 Remington was introduced by Remington Arms Company in 1955 as a necked down version of the .257 Roberts. Rifles marked .244 Remington have a 1 in 12-inch (300 mm) twist and it presented a problem stabilising heavier bullets. It was rebranded by Remington in...

The 6mm PPC (Palmisano & Pindel Cartridge), was designed for benchrest shooting and is a necked-up version of the .22 PPC which is in turn based on a .220 Russian

   Match cartridge based on the 243 WSSM case with a rebated rim to fit the 6mm PPC boltface

   Ackley design specifically for single shot rifles and made from shortened 30-40 Krag cases necked to 6mm with a 28 degree shoulder.

Wildcat cartridge based on the NORMA BR case

American wildcatters began fiddling with the 6mm's after WW2. This is one of several versions that exist of these experiments and were popular with Bench Rest shooters. Based on the 250 Savage necked down, but differs from the Donaldson version as it retains the...

Harvey Donaldson of Fultonville NY is regarded as one of the fathers of modern bench rest shooting. This is one of several versions based on the 250 Savage case. The Donaldson version has a ¼" shortened case with the shoulder pushed back.   

The 6mm HAGAR was derived from the 30 Remington and it has the same case head diameter as the 6.8 SPC, also a 30 Remington derivative. The cartridge was developed by John Harrison, a prominent match rifle shooter and Sid Goodling, a well-respected bench-rest gunsmith...

New line of 5 cartridges based on the 30 M1 case. From the website: The Garin SureStrike System is a complete line of five highly efficient and accurate cartridges designed for varmint, small game and target pursuits. Differing only by specific neck diameter and...

The 6mm Dasher is an old wildcat caliber dating from 1999. During 2017, it was brought out by Norma as properly manufactured brass on the behest of American F Class shooter Shiraz Balolia, who has commissioned Norma to manufacture fully-formed 6mm Dasher brass, but it...

Relatively new, this is the 6.5 Creedmoor necked down to 6mm   

Match cartridge based on the 243 Win case with a 30° shoulder   

Wildcat based on the Remington Bench Rest case   

   Based on the 222 Remington Magnum case necked up to 6mm

   Wildcat by Gene Beggs of Odessa, TX on a modified 220 Russian case

Based on the 7mm Rem Mag necked down to 6mm   

Unknown belted round