Originally Posted by Botchbomber
I've once heard that the optimal fps would be around 330fps. A higher fps create more friction between BB and the air which in the long run lower your range.
So according to that theory (haven't really tested it myself) with a 400fps @ .20g . You should use heavier BB (ex: .25g) so your barrel fps is around 330.
I know there's some truth to this. When using 0.20 BB's @ 400fps, they go straight for a while, then do crazy things near then end of their flight path, like go off in crazy directions, etc.
Using a heavier BB corrects this.