There were and still are many 'wildcat' cartridges based on the 30-06 case shortened, necked up and down. The same with many other cartridges, such as the 8x57 [Germanyicon], 303 [Australiaicon and Canadaicon], 7,62x54 [Finlandicon], propriety Britishicon big game cartridges on which many well known commercial cartridges are based, etc.

Many 'brand new' cartridges can be traced back almost to 1900. The book 'Cartridges of the World' by Frank Barnes provides hours of enjoyment when you read the detail and compare the dimensions of cartridges. Fascinating to see your pet 'wildcat' that you are developing for a specific use already existed decades ago. You will be astounded how many cartridges share the basic head dimensions of the 8x57 Mauser cartridge family from 1888 and British H&H cartridges from about 1925.

A colleague of mine spent a lot of time on wildcatting a family of cartridges based on the 9,3 Brenneke; wasn't impressed when I showed him it had been done in Europe about 50 years before he started.

Some useless information:
The 8x57 line up - all commercial - starts with 6x57 and goes to 10,75x57.
30-06 starts with 25-06 and ends with 400 Whelen.
The 6,5x57 predates the 257 Roberts and they are basically the same.
Etc.