Is not momentum simply the kinetic energy at a given point in time?
At any rate, a BB with more mass will be less affected by gravity and air resistance and any other factors that can affect the ballistics of an airsoft BB than a lighter BB. The result is shots that are more consistant over their range, can and do have increased energy when fired and will retain their energy longer than a lighter BB. This retained energy is what causes the increased impact energy at the target.
A BB that flies all over the place may physically go farther than a heavier BB, but it's is useless for play and when it does finally strike a target, it has bled away so much of it's energy that it's impact is much less noticeable.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.