Currently, the GMG in the speedboat and Hunter/Ifrit GMG has the ability to be zeroed to 100m,200m,300m,400m,600m,800m,1000m,1200m
(I might be mistaken on the lower range increments)
This is too small and inaccurate to provide fire support with an GMG at medium and long ranges.

I suggest that there will be minimum increments of 100m, so that you could zero the HMG to ranges:
100m,200m,300m,400m,500m,600m,700m,800m,900m,1000m,1100m,1200m

50m increments would also be even better but that might be too much, a solution to this problem would be adding options to do increments of 25/50m, or adding FCS like in ArmA 2, which would make sense seeing as the GMGs are advanced models, so it'd make sense that they have a FCS system.