It depends on the condition. Heavier pellets are more effective if the conditions are windy, Heavier pellets can easily push through the air which results in less energy loss for better penetration. The two most popular calibers are .177 and .22. Therefore, in situations under the heavy wind, heavier pellets are reliably more accurate. In normal conditions, you won’t significantly see the difference. However, heavier pellets are slightly more accurate still because it can conserve more energy as it travels through the air.