I agree with Sht_LE.
I have been looking at the same information and think there is either a problem with the identification or the measurements of the bullet diameter.
I am no expert on this cartridge but it does not match the 276 Pederson descriptions in the above mentioned reference.
Perhaps the cartridge started life originally as a 276 Pederson but is some type of wildcat.
The case length, rim diameter, base diameter, and case length match some of the Pederson case types but the bullet diameter, neck diameter, and case taper are real problems for this to be a 276 Pederson. The above example is basically a straight walled case not a tapered case like the Pederson.
Another problem, where does a .270 bullet diameter come from? A 270 Winchester has a .277 inch diameter bullet and a 6.5 mm has a .264 inch diameter, while the 7mm has a .284 inch diameter. The 276 Pederson had a bullet diameter of .283 to .286 inches.
From the dimensions provided this cartridge would seem more like the 7mm-08 having a 2.035 case length and .473 inch rim diameter. Maximum on the neck diameter for the 7mm-08 is about .314 inch but with a little outside neck turning this difference might be eliminated.
The 276 Pederson FB-9892 case could have been a starting point as this ammunition was released to the public under the CMP and those dimensions are closest to the case dimensions in question but still doesn’t explain the 270 inch bullet diameter.
I am not excluding either possibility but I don’t think we have all the information yet.