[lurkingknight]

if you want high degree of accuracy and precision at farther ranges you need to use heavier BBs. The trade off is the velocity of your round, but at the end of the flight path, it's carrying more speed because it's heavier so you make up for it there. A heavier round will be less prone to being blown by a breeze or mousefarts, also more likely to not have air bubbles that throw off the balance as it spins through the air.

A lighter bb doesn't carry as much momentum so air resistance will slow it down much faster than a heavier round.