What is your opinion of the new .25 airgun calibre? Does it have more hitting power for rabbits at longer ranges?

The .25 calibre is actually not new. It was a very popular calibre for smooth-bored airguns, such as the Gem and Britannia, produced just before and after the start of the last century. BSA made air rifles in .25 calibre before settling for the .22 as the standard sporting calibre.

The .25 is too heavy to use in air rifles producing muzzle energies within the British legal limit of 12ft/lb. The trajectory would not be flat enough at normal air rifle ranges, though it is ideal for short-range use such as rat shooting in barns. If you obtain a firearms certificate for a high-powered air rifle, then either a pre-charged pneumatic rifle firing a heavy 30- or so grain pellet or a spring-powered rifle using a lighter 18- to 20- grain pellet would make a very efficient hunting tool. Most gunshops store
.25 pellets weighing between 18 and 31 grains