We had plenty of the X8 FN rifles in Singapore during the 60's. Most of the back-room/rear echelon blokes had them. The Singapore Guard Regiment had them and the Governors Guard had highly polished rifles in gloss paint but not chromed (although the bayonet blades probably were). The REME LAD (LAD = Light Aid Detachments, the small REME workshops attached to the smaller units) at 25 Coy and 27 Coy had them too and the Military Police/ADP post at Nee Soon still had No5 rifles in their armoury. 40 Base had the usual racks of FN spares. The big shooting competitions always fielded a mixed bag of kit as we had .303 and L4 Brens, FN's and L1A1's Owens, Sterlings and AR15's
I seem to recall that the original trials FN bayonets slid down that long dovetailed lug on the barrel as they incorporated a sort of spring loaded recoil buffer thinggy that was supposed to allow the bayonet to slide on this as the rifle recoiled and ........... anyway, it was supposed to make it as accurate with the sliding bayonet as without a bayonet - so said! I didn't understand it then and don't understand it now. It' still a weight acting as a damper on a vibrating barrel. Sorry to go on!
Just a thought but is my assumption about this right or a load of crap, told to us my Mr Amto at 40 Base