I found something on google.. could help some newbies around
general advice is that you should bring with you a bottle of 0.25g BBs if wind is relatively mild. On the other hand, either stay home or bring with you a bottle of 0.30g BBs in case it is extremely windy out there.
Don't shoot long range when wind becomes a concern. Keep in mind: as long as your target is close enough, you stand a higher chance of hitting it. Based on our experience, any distance over 20M is too much for stock guns under heavy wind given the fact that stock guns are not powerful enough to push heavier BBs. On the other hand, if you all are using upgraded guns with FPS closer to the 400 level and airsoft 0.25/0.30g BBs, accuracy within 30-35M can still be achievable. -- Airsoft Tactics Manual, p. 48