All foregrips in the game are described as:
Aids in the manipulation of the firearm.
The V3 can be found in northern La Cruz province in a cartel outpost. The accessory case is inside the armoury in the centre of the outpost.
There are 15 bad guys at this outpost including a sniper and a lieutenant. I approached this at night time along the main road from the east, and this outpost is on a hilltop with buildings at multiple tiers above you as you face it from the road. Night time is a great time to collect accessories from an outpost, as the enemies congregate to eat or sleep, and of course it’s much harder for them to spot you. I managed to sneak all the way in without disturbing or taking out anybody.
The foregrip attachments (from the ‘Vertical Foregrip’ to the ‘Foregrip V4’) all provide the same benefit and trade-off, just to varying degrees. Each improves handling while sacrificing a little accuracy.
The V3 is an improvement on the Foregrip V2 found in Pucara and which foregrip you choose will depend on the balance you strive for with your gun stats. For more foregrip accessories, check out the Vertical Foregrip found in Itacua, or go for the V4 which you can pick up in Monte Puncu.
Personally, I like to rock a foregrip on an LMG or shotgun for the added mobility.