.40 gram BBs and higher are heavier weight BBs that are specifically designed for airsoft sniper rifles. The increased weight of these BBs provides increased accuracy and stability when shooting at longer ranges, making them ideal for airsoft sniping. It is important to note that using heavier BBs in other types of airsoft guns, such as AEGs or shotguns, could result in damage to the gun or decreased performance. It is always recommended to consult the manufacturer's specifications for your airsoft gun before choosing the appropriate weight of BBs to use.