From Wikipedia: https://en.wikipedia.org/wiki/.270_Winchester
The .270 Winchester is a rifle cartridge developed by Winchester Repeating Arms Company in 1923 and unveiled in 1925 as a chambering for their bolt-action Model 54. The cartridge is the same length as the .280 Remington, both of which are longer than the .30-06 Springfield. The .270, .280, and .30-06 were all derived from the .30-03 parent case that came from the German 8x57 Mauser case which itself was based on the earlier 7x57 Mauser case. The .270 Winchester uses a .270 inch (6.86 mm) bore diameter and a .277 inch (7.04 mm) bullet diameter.