Correct, now get over to the US forums and put some of those internet gurus right please.
Ammo is built to a standard, if that standard introduces variations or improvements then users are briefed on it and sights adjusted.
Its not like the leap between .303 Mk6 and 7 where new magazine platforms and rear sights were needed.
I don't know what your sources are, but the MOD did not specifically select RUAG to manufacture the ammunition for the L115A3. It just happens to be that they produce ammunition of a sufficient quality to be awarded a contract. The procurement process could quite easily go somewhere else.