Okay you wanna know the reason people upgrade to heavey bbs? Its cuz when a bb of .20 gram weight is shot at 330fps it is accurate for X distance. Take that same gun and shoot .28 gram bbs and it will be more accurate for X minus 10-15 feet. Take the .20 gram bb and shoot it at 380fps and it is now unstable in flight and accurate for X yet flies another 10-15 feet unpredictably. With the same 380fps shoot the .28 gram, it flies accurate for X plus 10 feet.
The hypothetical variance is just that, a variance. By no means is that data precise in its form but it is accurate. The facts stand firm with this and though I use .25 gram in a 380fps gun I see my need for .28 or .30 gram bbs. It comes down to the gun and its opperational prime. We often look to the standards set by our peers but forget that our peers all have different tools.