UKAPU member Tim Jacobs has made up this useful chart which shows the velocity of various weight BBs at 1.3J and 2.5J (the new legal power limits for airsoft). It’s a nice way to illustrate the point that with heavier BBs the permissible muzzle velocity is greatly reduced.
I’d imagine there’s a fair few people who currently own airsoft replicas that are set up to fire at just below the common site limit of 350fps on a 0.20g BB, yet some of those replicas could fire 0.25g BBs at more than 335fps, which is over the 1.3J legal limit.
Sadly there’s still been no PCA clarifications from the government. With the commencement orders for the firearms provisions supposedly due to be issued in the Spring, this is completely unreasonable. UKAPU and UKARA were promised in March last year that these issues would be looked at, and both organisations continue to pursue the matter.