Joule Creep

In theory a gun's muzzle energy in joules should stay roughly constant across BB weights, since energy is what a well-designed hop-up and barrel are actually transferring. In practice many guns — especially ones with an aggressive or poorly matched hop-up unit — deliver measurably more energy with heavier BBs than the number a light reference BB suggested.

This matters directly at chrono: a gun that reads safely under a field's limit on a 0.20g test BB can exceed it once loaded with 0.28g or 0.32g ammo. Responsible players chrono with the actual weight they intend to play, not just whatever the field happens to have on hand, and marshals increasingly ask for exactly that.

Testing across the actual range of BB weights a player intends to use, not just the field's single reference weight, is the only reliable way to know a gun's real behaviour, and some technicians do exactly that during a full internals rebuild.