The evolution of the .270 is well documented in a book entitled W.R.A. Co. (Winchester Repeating Arms Company): Headstamped Cartridges and Their Variations, by Daniel L. Shuey. There is even a photo of the orginal Winchester "Euro-Rifle." Now, whether Winchester borrowed the .270 bullet diameter is another question, but it is generally agreed among Winchester historians that after WWI Winchester decided on .270 to make sure the thousands of military 7x57's then in America (some on pre-98 Mauser actions) couldn't be rechambered for the Winchester round. Where they got the inspiration is anybody's guess, but there have been many cases of parallel evolution in rifle cartridges.
