The lighter the ammunition used the quicker the round will slow down. A .3 or .4 is able to hold its momentum and can punch through the air with more ease than a lighter BB. A .25 for example will have a much higher starting velocity but will slow down much faster as well. A .4 will have a slower initial velocity but will retain that velocity much better than the lighter BB.
It would be something like this in numbers:
.40g Starts at 450FPS ------ .40g at 100' is 430FPS ------ .40g at 200' is 400FPS ------ .40g at 300' is 350FPS
.20g Starts at 550FPS ------ .25g at 100' is 400FPS ------ .25g at 200' is 325FPS ------ .25g at 300' is 220FPS
None of that data is real just showing you how the BB acts in the air. You'll notice that the .25 has the advantage of velocity up to around 150'.
It would be something like this in numbers:
.40g Starts at 450FPS ------ .40g at 100' is 430FPS ------ .40g at 200' is 400FPS ------ .40g at 300' is 350FPS
.20g Starts at 550FPS ------ .25g at 100' is 400FPS ------ .25g at 200' is 325FPS ------ .25g at 300' is 220FPS
None of that data is real just showing you how the BB acts in the air. You'll notice that the .25 has the advantage of velocity up to around 150'.
