As I understand it, fuselage reference line (FRL) coincides with A-G reticle set to 0 mils and all the guns should be boresighted to FRL.
After some testing I get that the different guns are boresighted accordingly:
Internal: ~50 mils
Fuselage mounted: ~24 mils
Wing mounted: ~0 mils
So, internal (nose) and fuselage mounted gun are not boresighted correctly.