In 1919 Winchester rifle designer T.C. Johnson developed a 6.8mm projectiled cartridge designed around the 30-06 case. It was introduced in a limited run hand made rifle known as the "Winchester Imperial Sporting Rifle".
The Imperial was also known as the Model 51 Winchester.
Full scale production of a mass produced model was not begun until around 1925, due to a little trickery on the part of their competitor Remington.
What famous cartridge was born from this Winchester project and what were the next two model numbers (evolutionary steps) for this famous rifle design?