You need to look at some different Webly models online. There are lots of good pics.
Your revolver is likely one of the RIC or even earlier models. They aren't as strong as the later Number series.
Most of the Spanish and Belgium copies I've seen have been finished very well and shoot well. They just don't tend to be as robust as their British made counterparts.
Unless you have a mold that has been custom made for the bore diameter of your barrel, you might not get decent accuracy from flat base bullets that may be slightly small for your bore.
Jethunter, a poster on this site makes some very nice "hollow base" bullets for the .455 barrels.
The holow base promotes better obturation of the skirts into the rifling.