Originally Posted by Heerven
Is it not the opposite? Lighter mean less energy needed to spin the BB, no?
Yes but because its so light it has to spin at a remarkable speed to generate enough gyroscopic force and thus the barrel has to be coarsely rifled. Given the weights of about 0.2-0.4g and low apparent muzzel velocities, it would have to be rifled so coarse it would score the surface of the bb and likely sheer the grooves off it.