In the cartridge world, there are not a lot of orphan creations. Almost all of the known cartridges came from another cartridge design, or started a family of cartridges.
For example, of early example of a semi-auto pistol cartridge is the 7.65x 25mm Borchardt, created around 1893. This case was the mother of the 7.63x25 Mauser, 7.62x25 Tokarev, and 7.65 x 21 Parabellum (30 Luger). The 7.65 x 21 Parabellum (30 Luger) is the parent case of the 9 mm Parabellum; simply a 7.65x21 without a neck and a .355 mm bullet inserted.
The 7.62 x 51 mm was the result of the U.S. Army's attempt to replace the 30-06 with something smaller and lighter. They started with a .300 Savage case and created the T-65, a.k.a. --7.62x51mm. We all know this was commercialized into the 308 Winchester. Here's where the family really blows up.. and down. The .308 Win has been sized up and down every-which-way possible. The .243 Winchester, .358 Winchester, 7mm-08, .260 Remington, and the brand new.338 Federal. These are just the commercial members of the family. There are .20, .22, improved, shortened, etc wildcats out there
Now, one of the biggest families out there belongs to the little known black powder, .38-55 Winchester. This is the daddy of one of the most popular metallic cartridges ever...the 30-30 Winchester. The 30-30 led to the .32 Winchester Special, .22 Savage High power, 7-30 Waters, .25-35 Winchester, .219 Zipper, .22 Accelerator and .375 Winchester. The .30-30 is well over 120 years old and has been stretched, cut, sized up and down, poked and prodded probably more then any other cartridge out there.
Another huge family is the 8mm Mauser, also called the 8x57 Mauser. This momma cartridge begot the 7x57 Mauser, 9x57 Mauser, 6.5x57 Mauser, 6 mm Remington, 5.6x57 mm, 9x57 Mauser, 9.xx57 Mauser, and .257 Roberts/257 Roberts Improved. Some historians states that the 30-03 Springfield is simply a larger caliber copy of the 7mm Mauser, or smaller copy of the 8 mm Mauser. If you believe this, then the 8 mm Mauser is the grandmother of 30-06 which has an impressive family of its own, including: 35 Whelen, 338-06, .25-06 Remington, .270 Winchester, 6mm-06, 6.5mm-06 and 8mm-06, and .280 Remington.
For my final family.. the 375 H&H Magnum...
.244 H&H Magnum, 7x61 Sharpe & Hart Super, 7mm Remington Magnum, 7mm Weatherby Magnum, .257 Weatherby Magnum, .275 H&H Magnum, 7mm Shooting Times Westerner, .300 H&H Magnum, .264 Winchester Magnum, .270 Weatherby Magnum, .300 Weatherby Magnum, 8mm Remington Magnum, 6.5mm Remington Magnum, .350 Remington Magnum .340 Weatherby Magnum, .375 Weatherby Magnum, .400 H&H Magnum, .308 Norma Magnum, .338 Winchester Magnum .358 Norma Magnum, .416 Remington Magnum, .458 Lott, .465 H&H Magnum, .300 Winchester Magnum, and the .458 Winchester Magnum.
There are a ton of other families out there, for example, 45 ACP, .222 Remington, 10mm (10x25 mm), .416 Rigby, 400 Nitro, etc, etc, etc. It can be fun to trace origins of common place things, like cartridges to see where they came from..a little like Indiana Jones'ing through the web for facts and clues....
