I can only speak from personal experience, with my two L42A1 and Enfield Enforcer. The ammunition that was “originally” used was Match/Sniper grade Green Spot RG 7.62mm L2A2 144grn ammunition. I have personally been using L2A2 RG 13.5.92W (Sniper) from ranges 200 yards to1,100 yards through the L42A1’s with good results. I don’t feel that the (sniper) ammo out shoots the normal L2A2 ammunition, to any greater extent once you have zeroed to a “BATCH” stick with it.
I have also used Black Spot 7.62mm RG L42A1, L42A2 & L42A3, with 155 grn with excellent results. I feel that the heavier 155 grn round produce a more consistent shoot, and thus the accuracy is increased compared to the L2A2 144grn especially at the longer ranges (600 – 1,100 yards) I am not a hand loader so cannot comment on this special, area of ammunition production.
I am still using RG L42A3 18.8.08 Black Spot ammunition and hitting V-Bulls, at 1000 yards. Much to the surprise to people around me, with all there new fangled equipment and special sight etc…..