
Here is a pair of .450 RICs, both from the Metropolitan Police batch. Moe's is in finer condition. I also use shortened Mk. II cases. Apparently some .450s will accept .455 Mk. II cases. These won't. Once cases are prepared, reloading them is no different than any other pistol cartridge. They are fine shooters.
Cases can also be made from .45 Colt. More complicated, though. Rims must be thinned from the front, in addition to substantial trimming. The smaller rim diameter is not an issue, because these use the rod ejection system.
Big advantage of the top break Webleys is simultaneous ejection, rather than poking them out one at a time.
Preparing ammunition for sale is manufacturing, and requires an ammunition manufacturing licence. There is also a substantial liability issue.