You can read about the 6.8mm Chinese in Ludwig Olson's book, "Mauser Bolt Rifles".
I am not totally sure about this one, but I have my own theory about how the .270 Winchester was developed.
The round came out in 1925, and prior to this time, Winchester was looking for a new round based on the .30-06 case. The Germans had already come out with the 7x64mm, so Winchester was beaten to the punch insofar as the 7mm bore was concerned. Then again, it was a metric diameter and perhaps that would not sell.
And Charles Newton had already necked down the .30-06 and come up with the .256 Newton. ( a 6.5mm round)
So, here is what I think Winchester did. They took the bullet diameter of the .30-06 and they multiplied it by 90%. ( .90 multiplied by .308 equals .277) And that is how the .270 bore diameter got started. ( I think)
I bet that the Chinese round and the .270 were independant developments.
I thought about the 6.8mm Chinese and I bet I know what the Chinese were thinking about.
The Chinese used the 8mm Mauser and this round has some serious recoil. It certainly would be a bit much for troops of shorter stature. The Japanese were using the 6.5x50 and this light recoiling cartridge was a wonderful round. The Chinese probably wanted a round of similar ballistic properties, but they had a problem.
The Japanese were a major threat to China and it would not have made sense for the Chinese to adopt a 6.5mm cartridge. Had they done so, the Japanese would have been able to make use of captured Chinese ammuntion components.
So the next best thing to a new 6.5mm cartridge would have been to split the difference between 6.5mm and 7mm. And that is probably how the 6.8mm came about.
But adopting a new cartridge is a serious undertaking and the round was never adopted. But had I been a Chinese ammo designer in the early 20th century, that's what I would have done.
Mad, that is some awesome thinking on both theories. You've made me a believer on both of them. In a way, the Japanese went through the same thing from the opposite point of view when they wanted something bigger than the 6.5mm but had to stay within the constraints of tolerable recoil and picked the 7.7mm round. I never thought of it working the other way around though.
The theory about how the .270 Win was invented made a lot of sense too.
Most of the countries I mentioned issued larger bore rifles to their machinegunners or soldiers in machine gun regiments.
One of the rarest Mausers is the Swedish 98 chambered in 8x63mm Bofors caliber. This round made the .30-06 look like a white mouse. These Swedish Model 98s were made by Mauser in the mid 1930s and they are super rare and valuable. They appeared on the US surplus market in the 1960s and most fell into the hands of Bubba.