The 270 Newton caliber is most probably not one of Charles Newtons inventions. It would seem that it came along much later than the original 30, 35, 40 and famous 256 (6.5-06) Newton calibers.
This case is by Speer, but apparently Western also made it. Speer bullets and consequently ammo came along in the late 1940’s. The 30 Newton was designed back before WWI in the nineteen teens. In Bruce Jennings’ book “Charles Newton, the Father of High Velocity”, no mention is made of the 270 Newton. So it doesn’t make sense that the 270 Newton was made in 1915 to 1919 as were the rest of the Newtons. Maybe a product of Speer bullets/ammunition in the late forties. On page 98 there is mention of a 280 Newton, but Jennings states that “The 280 Newton is about as evasive as the Holy Grail.”
I found this on the outdoorsdirectory forum – “In the latest addition of his book on Newton arms Larry Wales states on page 180 that “The 270 Newton made by Speer and designed by N. S. Hollingshead was the only non-Newton cartridge to be stamped with the Newton name”.
Source: Armory Publications