If they don't deviate some from the MOD specification there will be some rifles the barrels cannot be fitted to. Then people will be back to using rings to take up the space at the shoulder when the metal on the shoulder could have been left long.
With the exhaustion of Britishmilitary ammo the only ammo close to fitting the huge chambers well is the stuff made by PPU. The #4 barrels would benefit from having smaller diameter chambers unless you just want everything as mud proof as an original. With the large chamber case life will be shortened.