p.s. were a person to have the druthers, he could probably fashion a pretty respectable facsimile of a .280 british round from .35 remington brass ...

friends:

if you look to your newest edition of cartridges of the world, you will find that the .280 british as initially fabricated had case rim and case head dimensions very similar to the .35 remington, a round extent pretty much contemporaneously with the model 8 remington auto rifle.  

this was a long recoil arm designed by john m. browning, and they were made a long time, and a lot of them are still in use.  good guns.  they will kick the holy bejesus out of you.

but, the .35 remington (cartridge) i think has enough dimension where a resizing die would place the shoulder on a .280 british so that you would not have to do any fire forming.  

as to the .276 pedersen, i think the 7.35 terni/mannlicher carcano might be suitable for it, or at least give you a similar enough round to "fake" it pretty well.

or, you could just be content, as i am, to mess around with the 6.8mm remington spc if you are looking for an intermediate round to go onto an ar-15 platform.

john jay @ 12.24.2011

p.s.  you can get saami  cartridge dimension drawings/schematics at this link,  http://www.saami.org/specifications_and_information/index.cfm?page=CC