I know that they’re two different rounds, designed for two different means to the same end. I think I heard that .270 was a light bullet, shot at a fairly flat trajectory and having a max accurate range out to about 600 yards. .280 had a heavy bullet and was attempting to bridge the gap between a true intermediate round and a full power round. Is this true or am I missing the mark here?
I think your summary is more or less correct!
You can read the rather mysterious story of the British Small Arms Calibre Panel, and what happened next, starting on page 15 of this web article: http://quarryhs.co.uk/GPC.pdf
Ballistic data on the .270 is on page 17, on the .280 developments on page 21.
Are there any way to get exact dimensions on the .270 to maybe remake it.