[L473ncy]

Since pretty much every BB has an "air bubble" in them you also want to make sure that it's in the "centre" or close to the centre. It would make sense that a BB with an air bubble that's off to the side or something when it passes through the hop up and down the barrel will have a weird flight path since the weight isn't totally distributed evenly. Simple high school physics.

Not sure if the above made sense but in a nutshell you want your BB to have as small of an "air bubble" in it as possible and preferably have it in the dead centre.