Ironic that you mention the GPMG/FN MAG58 in the OHF role BAR. I was one of the Armourers on the team investigating its suitability to replace the Vickers guns. We didn't know too much about the wear patterns of the GPMG's or the tripods at the time. So there was nothing to compare it with really. Our first GPMG's were all BL 64 or 65....., BelgiumLiege, 1964 or 65 made guns. Some of the later ones were designated L7A1 made in Belgium before full production got underway at Enfield. Some of the old BL64 and 5 guns were still in service, upgraded to later spec several times in the 2000's
The buffered tripod was deemed to be a bit of a problem as were the mounting pin holes in the gun and tripod. I left the team part way through but it seems to have been acceptable. But as a result of the trials, the tighter barrel nut (the No2 barrel nut) was introduced to tighten up perfect 0- but loose - barrels.
What a magnificent bit of kit the GPMG turned out to be. I'm sure that it'll take the crown away from the Bren, at 66 years service, for length of service in the UKmilitary. I THINK, as someone said to me recently, that the prize must go to Bedford trucks..... But that's not comparing like for like!
We also had a Saracen APC painted in large yellow and black stripes plus an old up-armoured Centurion tank that would drive into the 'troop zone' and up to the fall of shot area to ascertain the new safety areas for the 762 ammo. The drivers, signalers and commanders would hear the clang of bullet strikes as they got into the troop zones. I bet that they wouldn't do that now...... I wonder if there's a 5.56mm LMG in the OHF role anywhere........?