That could be due to the different Jet fuel used, u know
different Type of Jet fuel got diff Density but the volume is
fixed, so, that could lead to different weight
If we consider the max external fuel load of 6800 kg (3 tanks of
2000L + 2 tanks of 1250 L = 8500 L) that gives us a fuel density of
0.8
If we apply that density to the internal tanks we get a volume of
5875 L
