the foregrip reduces horizontal sway when firing, but it reduces the actual accuracy and increases vertical sway. or something like that. comparing foregrip to no foregrip
if you look at the Spread category, the one without foregrip is slightly better.
the Recoil category shows where the foregrip helps. its not much but you can see a little bit of difference in the shot dispersion charts. (some guns there are huge differences here) Same charts comparing foregrip to heavy barrel